That's the new look. Mozilla has had a lot of feedback pro and con, but I don't know whether Firefox 90 will have any modification to the tab bar design or menu item spacing. If you want to roll back or modify some of these changes, I can give you a quick short-term workaround, but a more durable solution will require more work. '''** Tab Bar Layout **''' '''''Temporary Fix''''' For testing purposes, there is a preference to switch the tab bar and address bar between new style and old style. This is not expected to continue past Firefox 90, but maybe you want to use it for now. (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button accepting the risk. (2) In the search box in the page, type or paste '''browser.proton.enabled''' and pause while the list is filtered (3) Double-click the preference to switch between '''true''' (new style) and '''false''' (old style) '''''Longer Term Community Workaround''''' This involves setting up a userChrome.css file. I have a rules builder that will get more features throughout the month. By the time the above preference is removed, it should be mature. If you want to take a sneak peek now: * https://www.userchrome.org/firefox-89-styling-proton-ui.html#tabstyler * https://www.userchrome.org/how-create-userchrome-css.html '''** Menu Item Spacing **''' '''''Temporary Fix''''' For testing purposes, the developers left a preference in Firefox 89 to switch between new style and old style menus: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button accepting the risk. (2) In the search box in the page, type or paste '''browser.proton.contextmenus.enabled''' and pause while the list is filtered (3) Double-click the preference to switch between '''true''' (new style) and '''false''' (old style) ''If some menus look wrong after this change, you probably need to do a regular exit/restart of Firefox to complete the change.'' '''''Longer Term Community Workaround''''' This involves setting up a userChrome.css file. The full instructions are in the following thread: https://support.mozilla.org/questions/1337841