FF 45.2 ESR (latest that will install on this machine with Lucid 5.2.8 Linux) sometimes froze the system, more often crashed without any error message or from any particular action, except being more common with busy ad-laden sites. Crash Reporter has never ever made a report on this system. The FF crash will sometimes take down unrelated text-editing or image-viewing X-windows. Restarting FF (without reboot) sometimes works but sometimes causes another crash while loading the "Sesssion Restore" tab (without any IP connection). Usually 2nd or 3rd FF restarts (no reboot) allow continued operation, if no tabs from Session Restore are activated. However, in a recent case, starting FF after multiple reboots from system CD and no internet connection would cause immediate crash while loading the Session Resore tab, even if one attempted to stop that tab. Removing "...default/sessionstore-backups" and ".../sessionstore.bak" and ".../sessionCheckpoints.json" allowed FF to run. Any idea how the session restore procedure could cause repeatable crashes? Not familiar enough with Linux to know how to start FF under a trace procedure, but can put back the suspect files. Is there documentation on how to read those files in an editor?