Firefox 133+ have a revised userChrome implementation with regard to the tab bar: 1. the vbox with id #titlebar has been removed (without replacement), making it so that the tabcounter / menu is now always far to the right and tab width is narrower than the space reserved for tabs is, 2. private browsing: The indicator is now refered to by class instead of id - and it behaves slightly differently I've got a MR ready for 2., but 1. is a difficult one. I see the following options: a) increase tab width (and thus hide the private browsing indicator fully) and come up with another way to indicate you are in a private browsing session (idk, different tab background color?), b) keep tab with similar (enough) and unhide/bring back Firefox View - requiring making Firefox View mobile friendly first (it can be useful, especially for Sync users), c) find some way I have not come across yet to achieve the same effect the previous `padding-right: 30px` for #titlebar had to restore the known behaviour.