Add-ons using the techniques described in this document are considered a legacy technology in Firefox. Don't use these techniques to develop new add-ons. Use WebExtensions instead. If you maintain an add-on which uses the techniques described here, consider migrating it to use WebExtensions.
From Firefox 53 onwards, no new legacy add-ons will be accepted on addons.mozilla.org (AMO).
From Firefox 57 onwards, WebExtensions will be the only supported extension type, and Firefox will not load other types.
Even before Firefox 57, changes coming up in the Firefox platform will break many legacy extensions. These changes include multiprocess Firefox (e10s), sandboxing, and multiple content processes. Legacy extensions that are affected by these changes should migrate to WebExtensions if they can. See the "Compatibility Milestones" document for more.
A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.
Experimental
Modify styles using stylesheet files or CSS rules.
Globals
Constructors
Style(options)
The Style constructor creates an object that represents style modifications via stylesheet file(s) or/and CSS rules. Stylesheet file URL(s) are verified to be local to an add-on, while CSS rules are verified to be a string or array of strings.
The style created can be applied to a content by calling attach, and removed using detach. Those functions are part of content/mod module.
Parameters
options : object
Required options:
| Name | Type | |
|---|---|---|
| uri | string,array |
A string, or an array of strings, that represents local URI to stylesheet. |
| source | string,array |
A string, or an array of strings, that contains CSS rules. Those rules are applied after the rules in the stylesheet specified with |
Optional options:
| Name | Type | |
|---|---|---|
| type | string |
The type of the sheet. It accepts the following values: |
Style
Properties
source
An array of strings that contains the CSS rule(s) specified in the constructor's option; null if no source option was given to the constructor. This property is read-only.
uri
An array of strings that contains the stylesheet local URI(s) specified in the constructor's option; null if no uri option was given to the constructor. This property is read-only.
type
The type of the sheet. If no type is provided in constructor's option, it returns the default value, "author". This property is read-only.