If you mean this button:
...you can just remove that by clicking the "Remove from Toolbar" in the right-click menu (as shown).
If you still want to learn it, these two articles are good:
The video in the second article is important. Near the end of the video, they show the Browser Toolbox. With that, you can select a UI element in Firefox's UI to find out what the element's ID is. You will need the ID for writing the rule.
Yes i do, i did know that but i wanted my config to be easy to copy paste between machines. Still thanks for your input
Ah, well, I still don't want to discourage you from digging into the Firefox CSS customizations. It is a really useful tool to know.
But for this purpose, you probably want the about:config value browser.uiCustomization.state. It contains all information about UI placement customizations, which you probably want to copy-paste as a whole anyways.
You can create a user.js file in the profile directory to set the about:config value.
Ahh i havent hears of that, thank you very much!!!
I believe userChrome is deprecated and won't be read by Firefox anymore. I don't know if there is a replacement though.
You just have to set toolkit.legacyUserProfileCustomizations.stylesheets in about:config to true.
Yes, that does say "legacy", but I don't think, Mozilla cares to actually remove it. They mainly introduced that about:config flag to reduce startup time for the 99.9% of users that don't use a userChrome.css file...
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