Observer Notifications

Observer topics

The following are topics that you can observe during the course of an application. Unless otherwise noted you register for the topics using the nsIObserverService.

Application startup

These are the topics that you can observe on startup, in order of appearance.

If your component requires access to the user profile, or any services which require access to the profile (preferences, bookmarks, and so on) then a common pattern is to register with the nsICategoryManager for the app-startup topic which can be done in the component's registration code, and then in that notification register with the observer service for the profile-after-change notification. See Receiving startup notifications for more information about how this works.

Firefox 3.5 note

Starting in Firefox 3.5 components can simply register for the profile-after-change notification in nsICategoryManager.

Topic Description
*

Everything.  [nsObserverService.cpp]
Topic Description
xpcom-startup

Note: An extension can no longer be registered to receive this notification in Firefox 4 and later. See XPCOM changes in Gecko 2.0 for details.

Called when xpcom is initialized. Many things are not available for use at this point. To receive this notification you have to register with nsICategoryManager. The registered component is always retrieved as a singleton (That is getService() will be used to instantiate it).
app-startup

Note: An extension can no longer be registered to receive this notification in Firefox 4 and later. See XPCOM changes in Gecko 2.0 for details.

General event for application startup. To receive this notification you have to register with nsICategoryManager. Prepend "service," to the contract ID in the category registration to be invoked via getService() instead of createInstance().
profile-do-change This is fired after the profile has been selected. You will not be able to access user preferences, bookmarks, or anything that uses the profile folder until this event occurs. This occurs after any profile migration.
profile-after-change

This is fired after all the observers for profile-do-change have been notified.

Firefox 3.5 note

You can register with nsICategoryManager to receive this notification. Prior to Firefox 3.5, this was available to observers observing the app-startup/xpcom-startup notification.
final-ui-startup

Triggered just before the first window for the application is displayed.
sessionstore-windows-restored

Sent by the session restore process to indicate that all initial browser windows have opened. Note that while the window are open and the chrome loaded the tabs in the windows may still be being restored after this notification.

Note: This notification is specific to Firefox and SeaMonkey 2.0 applications

Application shutdown

These are the topics that you can observe on shutdown, in order of appearance.

Topic Description
quit-application-requested Something has requested that the application be shutdown. You can cancel the shutdown from here by setting aSubject.data to true (aSubject is the first parameter to your observer, the data value is an nsISupportsPRBool).
quit-application-granted All observers have agreed to the shutdown.
quit-application The application is about to quit. This can be in response to a normal shutdown, or a restart.
Note: The data value for this notification is either 'shutdown' or 'restart'.
profile-change-net-teardown The network connection is going offline at this point.
Note: The data value for this notification is always 'shutdown-persist'.
profile-change-teardown Part of the shutdown, profile data is still available at this point.
Note: The data value for this notification is always 'shutdown-persist'.
profile-before-change Called just before the profile is lost.
Note: The data value for this notification is always 'shutdown-persist'.
xpcom-will-shutdown Called just before xpcom-shutdown. Observer must not spin event loop.
xpcom-shutdown This is the end. Many things will not be available here.

Browser

These topics indicate interesting things that happen that the browser alerts you to.

Topic Description
browser:purge-session-history Sent when the sanitizer runs to purge all history and other information.
browser:purge-domain-data Sent after domain-specific history and other information have been purged. The data value is a string form of the domain.
browser-lastwindow-close-requested Sent when the browser wishes to close the last open browser window. When this is sent, it is possible that other windows may still be open, such as the download manager or preferences. The data value is an nsISupportsPRBool. Recipients may set this to true to abort the close.
browser-lastwindow-close-granted Sent when all interested parties have responded to the browser-lastwindow-close-requested notification and none of them requested that the close be aborted. After this is sent and handled, the browser window will close.
browser-delayed-startup-finished Sent when the browser window and all its components have been loaded and initialized.

Documents

These topics indicate notifications you can monitor related to DOM documents.

Topic Subject Data Description
chrome-document-global-created nsIDOMWindow null Sent immediately after a chrome document window has been set up, but before any script code has been executed. This lets extensions inject API into chrome windows as needed (see nsIDOMGlobalPropertyInitializer for an alternative method of doing this, which uses significantly less memory).
data is intentionally left blank.
content-document-global-created nsIDOMWindow origin Sent immediately after a web content document window has been set up, but before any script code has been executed. This lets extensions inject API into content windows as needed (see nsIDOMGlobalPropertyInitializer for an alternative method of doing this).
data is a string form of the origin (for use in security checks), eg "http://developer.mozilla.org".
document-element-inserted Document null Sent immediately after the root element of a document has been created, but before executing any script on it.
user-interaction-active nsIDOMWindow null

Sent once every 5000ms while this chrome document sees some kind of user activity (for example, keyboard or mouse events), and at the exact moment of the state transition from idle to active.
user-interaction-inactive nsIDOMWindow null

Sent when the chrome document has seen no user activity for a while. The notification is not repeated during a continuous inactivity period.

Windows

These topics indicate points of interest during the lifetime of a window.

Topic Data Description
dom-window-destroyed   Called just before a DOM window is destroyed.
inner-window-destroyed  null Called when an inner window is removed from the backward/forward cache. See Working With BFCache for information about the bfcache, and Inner and outer windows for details about how the window hierarchy works. Extensions that cache information about windows may wish to observe this so they can release information when the window is destroyed.  The window id can be obtained from subject.QueryInterface(Components.interfaces.nsISupportsPRUint64).data
outer-window-destroyed null Called when an outer window is disconnected from its docshell.  See Inner and outer windows for details about how the window hierarchy works. Extensions that cache information about windows may wish to observe this so they can release information when the window is destroyed.  The window id can be obtained from subject.QueryInterface(Components.interfaces.nsISupportsPRUint64).data
toplevel-window-ready   Called just after a new top level window has been opened and is ready, but has not yet loaded a document.
xul-window-destroyed   Called just before a XUL window is destroyed.
xul-window-registered   Called just after a top level XUL window is registered with the window mediator service.
xul-window-visible   Called just after a XUL window is made visible.

IO Notifications

These topics can be used to watch the IO service for useful information.

Topic Description
offline-requested Called to query whether the application can go offline. The attempt to go offline can be canceled.

Note: If your code chooses to cancel the attempt to go offline, it must notify the user.
network:offline-about-to-go-offline Called just before all network IO is taken offline.
network:offline-status-changed Called when the offline state has changed.
Note: The data value for this notification 'offline' or 'online' to indicate the new state.
network:link-status-changed Called when the network link status changes.

HTTP requests

These are the topics that you can observe during a HTTP request (see Setting HTTP request headers and Creating Sandboxed HTTP Connections). Both are passed an nsIHttpChannel as the subject parameter.

Topic Description
http-on-modify-request Called as a http request is made. The channel is available to allow you to modify headers and such. See this code snippet to learn how to get the tab that issued the request.
http-on-opening-request Similar to http-on-modify-request, but called earlier (synchronously during the channel's asyncOpen() call), and some channel attributes (proxyInfo) may be missing.  Use only if your observer must be called before asyncOpen returns.
http-on-examine-response Called after a response has been received from the web server. Headers are available on the channel. The response can be accessed and modified via nsITraceableChannel.
http-on-examine-cached-response Called instead of http-on-examine-response when a response will be read completely from the cache. Headers are available on the channel.
http-on-examine-merged-response Called instead of http-on-examine-response when a response will be read partially from cache, and partially from the network (HTTP 206 or 304 response). Headers are available on the channel.

Cookies

These topics indicate whenever a cookie has been changed (added, changed, cleared, or deleted) or its setting rejected by the browser. See nsICookieService for details.

Topic Description
cookie-changed Called upon a cookie change (added, changed, cleared, or deleted)
cookie-rejected Called when the setting of a cookie was rejected by the browser (per the user's preferences)

http-on-response-set-cookie

This is fired only when a cookie is created due to the presence of Set-Cookie header in the response header of any network request. This notification will come only after the "http-on-examine-response" is fired, but it will not always appear.

Download Manager

These topics indicate that events related to the Download Manager have occurred.

Topic Description
download-manager-ui-done Called when the list of downloads in the Download Manager windows finishes updating.  This can happen multiple times, such as when the window first opens, when multiple items are removed, and when entering private browsing mode.
download-manager-remove-download Called when a download of the list is removed or all the list is cleared. The subject will be the download id wrapped in nsISupportsPRUint32, for one download removed, or null for multi download remove, for example when the download list is cleared.

Extension Manager

Note: These notifications are no longer available starting with Gecko 2.0, instead use AddonManager.addAddonListener() to receive similar events.

This topic indicates when the extension manager performs some action. Note that any action will be taken the next time the application starts. See nsIExtensionManager for details.

Topic Data Description
em-action-requested item-installed A new extension has been installed.
em-action-requested item-upgraded A different version of an existing extension has been installed.
em-action-requested item-uninstalled An addon has been marked to be uninstalled.
em-action-requested item-enabled An addon has been enabled.
em-action-requested item-disabled An addon has been disabled.
em-action-requested item-cancel-action A previous action has been cancelled.

Idle Service

This topic indicates when actions related to the Idle Service, provided by the nsIIdleService interface. Unlike the user-interaction-active and user-interaction-inactive topics listed above, the Idle Service monitors user activity in general, whether related to the Mozilla application or not (acting somewhat like the user activity/inactivity events a screen saver would be interested in).

Topic Data Description
idle The length of time the user has been idle, in milliseconds. Sent when the user becomes idle.
idle-daily The length of time the user has been idle, in milliseconds. Sent once a day while the user is idle.
back The length of time the user has been idle, in milliseconds. Sent when the user returns from being idle.

Computer sleep and wake

This topic indicates when actions related to the computer going to sleep or waking up occur.  (Note: these notifications are not currently available on Linux.  See bug 758848.)

Topic Data Description
sleep_notification null Sent when the computer is going to sleep.
wake_notification null Sent when the computer is waking up.

Login Manager

This topic indicates when actions related to the Login Manager occur.

Topic Data Description
passwordmgr-found-form noAutofillForms A login is available for this form, but autofill of forms is disabled, so the form was not automatically filled out. 
passwordmgr-found-form autocompleteOff A login is available for this form, but autocomplete is disabled.
passwordmgr-storage-changed addLogin A login has been added to the Login Manager's database. The notification's subject is the login that was added to the database.
passwordmgr-storage-changed removeLogin A login was removed from the Login Manager's database. The notification's subject is the login that was removed from the database.
passwordmgr-storage-changed modifyLogin A login in the Login Manager's database was modified. The notification's subject is an array whose first entry is the old login and whose second entry is the new one.
passwordmgr-storage-changed removeAllLogins All logins have been removed from the Login Manager's database.
passwordmgr-storage-changed hostSavingEnabled Host saving has been enabled.
passwordmgr-storage-changed hostSavingDisabled Host saving has been disabled.

Places

This topic indicates when actions related to Places (the history and bookmarks database) occur.

Topic Data Description
places-autocomplete-feedback-updated   Sent when Places updates the location bar's autocompletion display.
places-connection-closed   Sent after Places has closed its database connection. Once this has been sent, no Places features will work.
places-connection-closing  

Sent as the last notification before the Places service closes its database connection.

Warning: This is for internal use only.
places-database-locked   The Places database is currently locked by a third-party process and cannot be opened.
places-favicons-expired   Sent when all favicons have been expired.
places-init-complete   The Places database has been successfully initialized. You should wait until this notification occurs before querying the places database.
places-maintenance-finished   Sent when maintenance of the Places database is complete; this is done periodically in the background to keep the Places database tidy.
places-shutdown   Sent when Places shuts down. If you are referencing instances of mozIStorageStatement referencing Places databases when this notification occurs, you should call their mozIStorageStatement.finalize() method
places-sync-finished   Sent when the Places database has been successfully flushed to disk.
places-will-close-connection  

Sent when the Places service is about to close its database connection. Only necessary cleanup tasks should run at this point, and nothing should be added to the database. In addition, after this has been sent, no Places APIs should be called.

Warning: This is for internal use only.

Session Store

These topics are used when actions related to Session Store occur.

Topic Data Description
sessionstore-state-read   Sent immediately after session store data is read and before it's used.
sessionstore-state-finalized   Sent immediately after the session is restored.
sessionstore-state-write   Sent immediately before the session store data is written to disk.
sessionstore-state-write-complete   Sent immediately after the session store data is written to disk.
sessionstore-state-purge-complete    

Private browsing

These topics indicate when actions related to private browsing occur.

Topic Data Description
private-browsing enter Sent when private browsing mode is activated.
private-browsing exit Sent when private browsing mode is deactivated.

Bookmarks

These topics indicate when actions related to bookmarks occur.

Topic Data Description
bookmarks-restore-begin json Sent just before bookmarks are restored from JSON.
bookmarks-restore-begin html Sent just before bookmarks are restored from HTML. If bookmarks will be restored into a specific folder, observers will be passed an nsISupportsPRInt64 through their subject parameters indicating the ID of the folder. The subject is null otherwise.
bookmarks-restore-begin html-initial Sent just before bookmarks are restored from HTML on initial import. If bookmarks are restored into a specific folder, observers will be passed an nsISupportsPRInt64 through their subject parameters indicating the ID of the folder. The subject is null otherwise.
bookmarks-restore-success json Sent just after bookmarks are restored from JSON.
bookmarks-restore-success html Sent just after bookmarks are restored from HTML. If bookmarks were restored into a specific folder, observers will be passed an nsISupportsPRInt64 through their subject parameters indicating the ID of the folder. The subject is null otherwise.
bookmarks-restore-success html-initial Sent just after bookmarks are restored from HTML on initial import. If bookmarks were restored into a specific folder, observers will be passed an nsISupportsPRInt64 through their subject parameters indicating the ID of the folder. The subject is null otherwise.
bookmarks-restore-failed json Sent when bookmarks could not be sucessfully restored from JSON.
bookmarks-restore-failed html Sent when bookmarks could not be successfully restored from HTML. If bookmarks were to have been restored into a specific folder, observers will be passed an nsISupportsPRInt64 through their subject parameters indicating the ID of the folder. The subject is null otherwise.
bookmarks-restore-failed html-initial Sent when bookmarks could not be successfully restored from HTML on intial import. If bookmarks were to have been restored into a specific folder, observers will be passed an nsISupportsPRInt64 through their subject parameters indicating the ID of the folder. The subject is null otherwise.

Themes

These topics indicate when actions related to themes occur.

Topic Data Description
lightweight-theme-preview-requested json Sent when the user requests to preview a lightweight theme, but before existing windows are styled with the new theme.
lightweight-theme-change-requested json Sent to indicate that the user has chosen a new theme in the add-ons manager, but before the change takes effect.
lightweight-theme-changed - Sent after the current theme is changed.
lightweight-theme-styling-update json Sent when the current theme being used is changed; this is sent even when the user is previewing a theme, not just when the theme is actually selected.
lightweight-theme-list-changed - The list of available lightweight themes has changed.

Developer tools

These topics let you know about things that have happened related to Firefox's built-in developer tools.

Topic Data Description
highlighter-ready -

Sent when the highlighter component is initialized.

Note: This is used by the Inspector to detect when it should begin its initialization process.
inspector-closed - Sent when the Inspector tool is closed.
inspector-editor-closed - Sent after the attribute-value editor has been closed.
inspector-editor-opened - Sent after the attribute-value editor has been opened and initialized.
inspector-editor-saved - Sent when changes have been saved in the attribute-value editor.
inspector-highlighting - Sent every time a different node in the page gets highlighted.
inspector-opened - Sent after the Inspector tool has finished its initialization.
inspector-ruleview-ready - Sent when the inspector's CSS Rule View is opened and initialized.
inspector-state-restored - Sent when the Inspector is re-opened after a tab switch.
inspector-treepanel-ready - Sent when the Inspector's Tree Panel is opened and initialized.
inspector-unhighlighting - Sent every time the highlighter stops highlighting a node.

Telemetry

Topic Data Description
gather-telemetry -

Note: This is obsolete and planned to be removed as it's not firing at the proper times.

Sent by the telemetry service when it's time to start gathering telemetry data, since the telemetry ping is coming soon.

Plugins

Topic Data Description
plugin-crashed - Sent when a plugin has crashed.

Message manager

Topic Subject Data Description
message-manager-disconnect nsIContentFrameMessageManager null

This notification is sent when a message manager disconnects.

The subject of the notification is the message manager that disconnected.

If you're using a message manager to communicate with a script that may be running in a different process, you might need to know when the message manager has disconnected from the other end of the conversation, so you can stop sending it messages or expecting to receive messages.

For example, suppose you've loaded a frame script into a tab using a browser message manager, and the user closes the tab. The frame script is unloaded and the browser message manager disconnects from it. By listening for message-manager-disconnect you will be informed when this happens.

Permission Manager

Topic Subject Data Description
perm-changed nsIPermission "deleted"/"added"/"changed"/"cleared"

This notification is sent when a permission changes.

The subject of the notification is the permission object.

Context menu

Topic Subject Data Description
content-contextmenu

An object containing two properties:

event
The event that triggered the context menu.
addonInfo
An empty object that add-ons can use to send data to the main process.
 null

This notification is sent when the context menu is displayed. It is sent, and received, in the content process: you can't listen to it in the chrome process.

It's used by the context-menu module in the Add-on SDK, to help send information to the context-menu code running in the chrome process when a context menu is displayed.

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