It probably would be sensible to backup firefox bookmarks or at least make copies of the firefox profile, as that contains the bookmarks and backups of bookmarks, and may be copied even if firefox is not open. It is good practice to back up bookmarks on a regular basis, and keep backups somewhere safe (outside firefox's program and profile paths)

• see backing up and restoring bookmarks

Have you already read firefox crashes
Note your crash ID report: https://crash-stats.mozilla.com/report/index/c239d837-853f-4a67-863a-909ff2111107
and signature : (empty signature)

Your crash is almost certainly due to software installed relating to Trusteer Rapport. There are many other threads on this forum about that crashing firefox. Trusteer are apparently aware of the problem, so check for updates, otherwise disable or uninstall it whilst you use firefox.

( If you need Trusteer for your banking consider trying firefox portable, because the software may be compatible with Firefox 3.6 try http://portableapps.com/apps/internet/firefox_portable/localization#legacy36 )

Edit

• Bugs have been filed already for Trusteer problems eg Bug696057 & 68152
• other threads include /questions/892720 which quotes a Trusteer reply. Also /questions/887181 & /questions/893097.
• and a search which is likely to show related posts is: https://support.mozilla.com/en-US/search?q=trusteer+crash&num_voted=0&num_votes=&asked_by=&answered_by=&q_tags=&created=0&created_date=&updated=0&updated_date=&sortby=0&a=1&w=2
• Trusteer has caused problems previously see http://kb.mozillazine.org/Firefox_crashes#Trusteer_Rapport
• comment also added in contributors forum /forums/contributors/707772

Yes it seems to be Trusteer Rapport that is the cause. Thanks for that stops me trying a host of other things

Glad to have helped.
Note the Mozillazine link in my post above provides instructions for disabling Trusteer.

P.S.
I have been made aware of this faq from Trusteer http://www.trusteer.com/support/en/my-browser-crashing and there is a posibility some crashes could be due to interactions with other Add-ons.

It would be worth testing Trusteer with firefox's safe mode and with other plugins disabled. It would be interesting to see if that works, and also what if any other Add-ons may be implicated in crashes involving Trusteer.

Thank you John99! I have stopped Trusteer Rapport and now Firefox is fine - not sure what TR even is, or whether we need it, but things are back to how they were. so thanks for you easy-to-follow help

I am glad your problem is solved, thanks for posting back to confirm that.

Trusteer Rapport is used by some Banks and some large retailers when verifying financial transactions by card, so it is something quite important to some users. Maybe you have more than one card and only one of those uses TR and then only on occasional transactions.