This option may be turned off? Also please check to see if there are any options on the computer that are closing software. Firefox Options > Tabs > Warn me when closing multiple tabs

Does Firefox crash (plante)?

If you have submitted crash reports then please post the IDs of one or more recent crash reports that have a "bp-" prefix:

• bp-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

You can find the IDs of the submitted crash reports on the about:crashes page.

• You can open the about:crashes page via the location bar, like you open a website, or open the crash reports page via "Help > Troubleshooting Information".

See:

• http://kb.mozillazine.org/Mozilla_Crash_Reporter
• https://support.mozilla.org/kb/Mozilla+Crash+Reporter