We are planning to deprecate the use by Firefox add-ons of the techniques described in this document.
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 instead.
Add-ons developed using these techniques might not work with multiprocess Firefox (e10s), which is already the default in Firefox Nightly and Firefox Developer Edition, and will soon be the default in Beta and Release versions of Firefox. We have documentation on making your add-ons multiprocess-compatible, but it will be more future-proof for you to migrate to WebExtensions.
A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.
Modify styles using stylesheet files or CSS rules.
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.
options : object
A string, or an array of strings, that represents local URI to stylesheet.
A string, or an array of strings, that contains CSS rules. Those rules are applied after the rules in the stylesheet specified with
The type of the sheet. It accepts the following values:
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.
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.
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.