Previously, this button only appeared when there were so many tabs that you couldn't see them all on the bar (left and right scroll buttons also appeared). Now you can use the Tab Manager all the time. If you want to roll back the change to only seeing it when the tab bar is overflowing, there is a setting for that: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button accepting the risk. ''More info on about:config:'' [[Configuration Editor for Firefox]]. ''The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.'' (2) In the search box in the page, type or paste '''browser.tabs.tabmanager.enabled''' and pause while the list is filtered (3) Double-click the preference to switch the value from true to false Please note that this only takes effect in new windows, or after you exit and restart Firefox.