What you really need to be doing is backing up all of your user data.

If you are backing up all of your Firefox profile to an external device your Firefox application would be protected. Bookmarks are an important asset, but so are your passwords, your options, your extensions, etc.

You can export your bookmarks to an HTML file on a USB thumb drive and access it almost anywhere on any browser without installing it on a borrowed system. You have to export with Firefox up, and you may be able to use Firefox in Safe mode. You can fix a lot of problems from within Safe Mode, I would see if Firefox works in Safe mode.

If the question is about where to grab your bookmarks so you can reinstall them if need be, your bookmarks are in places.sqlite along with history, but the bookmarks themselves are backed up each day you use Firefox in the bookmarkbackups directory as .json files which can be used to quickly replace all of your bookmarks in Firefox while Firefox is up.

See

• Browser will not start up - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Browser_will_not_start_up
• Safe Mode - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Safe_Mode
• Profile folder - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Profile
• Profile folder - Firefox - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Profile_folder_-_Firefox
• Bookmarks - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Bookmarks
• Sorting and rearranging bookmarks - Firefox - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Sorting_and_rearranging_bookmarks_-_Firefox
• Transferring data to a new profile - Firefox - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

A possible cause is security software (firewall) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.com/kb/Server+not+found
• https://support.mozilla.com/kb/Firewalls

See also:

• http://kb.mozillazine.org/Browser_will_not_start_up

found the bookmark backup files and reinstalled firefox... thanks!