Hellow, im trying to hide some element in firefox using userChrome. In perticular on left the the "View recent browsing accross windows and devices" how could i do that? Or what is a good resource to know how to learn this myself?
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.
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.