Hmm, when did this start? '''e10s''' One of the headline changes in Firefox 48+ is e10s, which separates the browser interface process from the page content process. The performance impact of this can vary a lot between systems: many users find it faster, some find it slower, for many it's neutral. Hopefully by the time all the kinks are worked out it will work smoothly for everyone. ''Are you using e10s?'' You can check whether you have this feature turned on as follows. Either: * "3-bar" menu button > "?" button > Troubleshooting Information * (menu bar) Help > Troubleshooting Information * type or paste about:support in the address bar and press Enter In the first table on the page, check the row for "Multiprocess Windows" and see whether the number on the left side of the fraction is greater than zero. If so, you are using e10s. ''If you are using e10s:'' To help evaluate whether that feature is causing this problem, you could turn it off as follows: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button promising to be careful. (2) In the search box above the list, type or paste '''autos''' and pause while the list is filtered (3) Double-click the '''browser.tabs.remote.autostart.2''' preference to switch the value from true to false ''Note: the exact name of the preference may vary, but it will start with browser.tabs.remote.autostart'' At your next Firefox startup, it should run in the traditional way. Any difference?