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Add-on dev: How can I edit Firefox UI CSS?

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  • 1 am na jafe-jafe bii
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  • i mujjee tontu mooy cor-el

dukevin
dukevin
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I'm developing an add-on for Firefox which will take the colors from the favicon of the current tab to color bits of the tab-bar dynamically.

I'm having trouble finding out how I can modify browser CSS, for example in the Browser Tool box console, this works perfectly fine: ```const activeTab = document.querySelector('.tabbrowser-tab[selected="true"] .tab-background'); activeTab.style.background = "rgb(0, 221, 255)";```

but when inputting this same code in my add-on, it cannot query that same selector (I've given it tabs and theme permissions). This also does not work as a stylesheet.

Can anyone point me to what I need to access the browser UI DOM?

I'm developing an add-on for Firefox which will take the colors from the favicon of the current tab to color bits of the tab-bar dynamically. I'm having trouble finding out how I can modify browser CSS, for example in the Browser Tool box console, this works perfectly fine: ```const activeTab = document.querySelector('.tabbrowser-tab[selected="true"] .tab-background'); activeTab.style.background = "rgb(0, 221, 255)";``` but when inputting this same code in my add-on, it cannot query that same selector (I've given it tabs and theme permissions). This also does not work as a stylesheet. Can anyone point me to what I need to access the browser UI DOM?

All Replies (2)

Paul
Paul
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Hi

You may wish to ask about this issue in the add-on developers forum at:

https://discourse.mozilla.org/c/add-ons/35

cor-el
cor-el
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Web extensions can't access content in the user interface like the Tab bar, they can only interact with webpage content. You can't do this via an extension, this can only be done via userChrome.css.