Hi Arnaud Dupuis, I'm not sure the title is your main issue in making the tab narrower: Firefox has a minimum tab width of 50 pixels (the default is 76, but you can reduce it by setting the browser.tabs.tabMinWidth to 50 in about:config). Hiding the title and having blank space there might be a bit more aesthetically pleasing, but if you want smaller tabs, there's a hack for that. I listed the steps in this post: 1290794#answer-1323279.

You can consider to open all tabs as pinned tab to only have the favicon.

You can find items like "Pin Tab" in the drop-down list that opens if you click the "Page actions" button (3-dot icon at the right end of the location/address bar).
You can right-click an item in the "Page actions" drop-down list to add its button to the location/address bar for easy access.

Thanks, the userChrome solution is the one for me. It should be more straightforward though...

Note that you can get issues if Firefox wants to add icons like when playing audio or view a video in PiP mode to a tab, so maybe test that.

well, pining every single tab is not acceptable (I have hundreds of tabs on multiple windows) so either it works or I will be forced to switch back to Chrome (I have no desire or intention of doing that).