Hi, do you mean the sidebar that you can optionally open on the left side (Ctrl+B) or the Toolbar you can optionally open below the address bar (Ctrl+Shift+B)? In another thread, someone mentioned there is a new option for the sidebar to "collapse" which I guess means to close itself, but that isn't happening on mine yet. Perhaps it is an experimental option that is currently in testing. To roll back your sidebar to the classic behavior, you could try the following: (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 '''sidebar.revamp''' and pause while the list is filtered (3) If the preference is set to true, double-click it (or click the Toggle button at the right end of the row) to switch the value from true to false Any difference?