theme_experiment
Type | Object |
---|---|
Mandatory | No |
Manifest version | 2 or higher |
Example |
json
|
This key enables the definition of experimental theme
key properties for the Firefox interface. These experiments are a precursor to proposing new theme features for inclusion in Firefox. Experimentation is done by:
- creating a stylesheet that defines mappings between internal CSS selectors for Firefox UI elements and arbitrary CSS variables. The CSS variables are then mapped in the
colors
,images
, andproperties
objects to newtheme
key properties. - (without a stylesheet) using
colors
,images
, andproperties
to map internal Firefox CSS selectors, such as--arrowpanel-dimmed
to newtheme
key properties. This option limits experimentation to UI components that are associated with an inbuilt CSS variable.
To discover the CSS selectors for Firefox UI elements or internal Firefox CSS variables use the browser toolbox.
Note: This key is only available for use in Firefox Developer Edition and Firefox Nightly channels and requires the extensions.experiments.enabled
preference to be enabled. In Firefox 73 and earlier, the extensions.legacy.enabled
had to be used instead.
Warning: This feature is experimental and could be subject to change.
Syntax
The theme_experiment key is an object that takes the following properties:
Name | Type | Description |
---|---|---|
stylesheet |
String |
Optional Name of a stylesheet providing mapping of Firefox UI element CSS selectors to CSS variables. |
images |
Object |
Optional
Mappings of CSS variables (as defined in Firefox or by the stylesheet
defined in |
colors |
Object |
Optional
Mappings of CSS variables (as defined in Firefox or by the stylesheet
defined in |
properties |
Object |
Optional
Mappings of CSS variables (as defined in Firefox or by the stylesheet
defined in |
Examples
This example uses a stylesheet named style.css
to provide the ability to set a color for the browser reload button in the theme
key.
The stylesheet defines:
css
#reload-button {
fill: var(--reload-button-color);
}
where #reload-button
is the Firefox internal CSS selector for the reload button and --reload-button-color
is an arbitrary name.
In the manifest.json
file, --reload-button-color
is then mapped to the name to be used in the colors
property of theme
:
json
"theme_experiment": {
"stylesheet": "style.css",
"colors": {
"reload_button": "--reload-button-color"
}
}
The argument reload_button
is used in the same way as any other theme
property:
json
"theme": {
"colors": {
"reload_button": "orange"
}
}
This has the effect of making the reload icon orange.
This property can also be used in browser.theme.update()
. images
and properties
work in a similar way to colors
.
Browser compatibility
BCD tables only load in the browser