So from there you will see the code I linked to in 'searchfox' exists in your directory too. Try changing the colours in the file browser/components/contextualidentity/content/usercontext.css for example and then try running firefox again. Also look at the [Browser Toolbox](https://developer.mozilla.org/en-US/docs/Tools/Browser_Toolbox] which allows you to debug the interface with the inspector much like the normal inspector for web pages. You can edit browser CSS and watch the result without running Firefox again. So the task then is to take the existing CSS and replace it with classes rather than attribute selectors. This requires manipulating the CSS file and also the JS that sets the attributes, this can be changes just to set classes.
Bug 1479433 Comment 7 Edit History
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So from there you will see the code I linked to in 'searchfox' exists in your directory too. Try changing the colours in the file browser/components/contextualidentity/content/usercontext.css for example and then try running firefox again. Also look at the [Browser Toolbox](https://developer.mozilla.org/en-US/docs/Tools/Browser_Toolbox) which allows you to debug the interface with the inspector much like the normal inspector for web pages. You can edit browser CSS and watch the result without running Firefox again. So the task then is to take the existing CSS and replace it with classes rather than attribute selectors. This requires manipulating the CSS file and also the JS that sets the attributes, this can be changes just to set classes.