Use "Firefox > Exit" (Windows: Firefox/File > Exit; Mac: Firefox > Quit Firefox; Linux: Firefox/File > Quit) to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar.

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 recent crash reports on the "Help > Troubleshooting Information" page (about:support).

• Click the "All Crash Reports" button on this page to open the about:crashes page and see all crash reports.

If necessary then you can open about: pages via the location bar.

See:

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

Usually Firefox will try to restore your previous session automatically after a crash. If that fails, then you get the embarrassing screen so you can avoid loading potential problem windows and tabs. Maybe the automatic restore is failing in some non-obvious, non-visible way?

I noticed you have customized the number of closed tabs that can be restore to a pretty large number (the default is 10):

browser.sessionstore.max_tabs_undo: 555 

It's possible that Firefox is reaching some limit on its ability to handle the amount of closed tabs being stored. If you don't really need that many, you could try a more modest number, like 50, and see whether that helps. If you want to try that:

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the search box above the list, type or paste sess and pause while the list is filtered

(3) Double-click the browser.sessionstore.max_tabs_undo preference and enter your preferred value

Thanks guys for your answers. Basically all works wonderfully well - I know I am pushing some limits here but I enjoy doing t his and also giving FF a real workout and perhaps contributing in some small way to testing. The number of max_tabs doesn't seem to make any difference. Like I said, other than the "embarrassing" message everything loads up fine! FF rules! A related issue is that, in trying to save my session, sometimes an error message comes up, and it has to do with some tab which contains some non-compliant script etc. The problem is, I never know which tab it is, so can't delete it and retry. What I sometimes do is use the "bookmarks all tabs" option. Would be nice if the save will work regardless or tell me which tab it doesn't like. This is part of a general problem with multi-tabs in FF - (and perhaps in other browsers?) which is, you don't know what happens in any particular tab - e.g. some tab starts singing or talking and I want to shut it up - but I don't know which one! Perhaps some future development will add features in this area.