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.
The following is a snippet to get isDefaultNamespace() supported across other browsers.
// http://www.w3.org/TR/DOM-Level-3-Core/core.html#Node3-isDefaultNamespace
// http://www.w3.org/TR/DOM-Level-3-Core/namespaces-algorithms.html#isDefaultNamespaceAlgo
function isDefaultNamespace(node, namespaceURI) {
if (node.isDefaultNamespace) {
return node.isDefaultNamespace(namespaceURI);
}
switch (node.nodeType) {
case 1: // ELEMENT_NODE
if (!node.prefix) {
return (node.namespaceURI === namespaceURI);
}
if (node.attributes.length) {
for (var i=0; i < node.attributes.length; i++) {
var att = node.attributes[i];
if (att.localName === 'xmlns') {
return att.value === namespaceURI;
}
}
}
if (node.parentNode) {
// EntityReferences may have to be skipped to get to it
return isDefaultNamespace(node.parentNode, namespaceURI);
}
else {
return false; // unknown;
}
case 9: // DOCUMENT_NODE
return isDefaultNamespace(node.documentElement, namespaceURI);
case 6: // ENTITY_NODE
case 12: // NOTATION_NODE
case 10: // DOCUMENT_TYPE_NODE
case 11: // DOCUMENT_FRAGMENT_NODE
return false; // unknown
case 2: // ATTRIBUTE_NODE:
if (node.ownerElement ) {
return isDefaultNamespace(node.ownerElement , namespaceURI);
}
else {
return false; // unknown
}
default:
if (node.parentNode) {
// EntityReferences may have to be skipped to get to it
return isDefaultNamespace(node.parentNode, namespaceURI);
}
else {
return false; // unknown
}
}
}