hello, can you try to replicate this behaviour when you launch firefox in safe mode once? if not, maybe an addon is interfering here... [[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems]]

You can check the home page setting.<br /> Firefox supports multiple home pages separated by '|' symbols. *Tools > Options > General > Startup: Home page *https://support.mozilla.org/kb/How+to+set+the+home+page ---- You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox profile folder that store session data. Delete the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox profile folder. *Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder) *http://kb.mozillazine.org/Profile_folder_-_Firefox *http://kb.mozillazine.org/Multiple_profile_files_created Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost and you will have to recreate them (make a note or bookmark them if possible).