You don't think 100 tabs is a bit much? Bookmarks can save pages that you want to revisit without taking a lot of resources.

I can not say I have noticed mass reports of instability.

Certainly some users keep 100 or more tabs open without problems. Although not bookmarked I remember a survey a couple of years ago that surprised me by just how many open tabs some users have.

What worries me about the practice is that session restore is not as robust as bookmarks, so there is potential to loose the open tabs. I did open about 600 recently without problems !!

Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from an existing profile to the new profile, but be careful not to copy corrupted files.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Even the advanced search on this Forum is rather primitive. I was trying to reproduce a users problem recently and so had several Firefox Windows one with 600 tabs open but Firefox worked ok for me. I can not find that thread at the moment. Having a lot of tabs open may not be the underlying cause, but it may make trouble shooting easier if the problem may be reproduced with one or only a few tabs open.

• New Profile
  First of all try cor-el's suggestion, if it is not already one of the many things you have tried. You may even wish to go further and set up multiple profiles for test purposes, & even may consider testing multiple versions in case for instance any problem is resolved by bug fixes not yet in the Release
  http://kb.mozillazine.org/Testing_pre-release_versions#Installing_multiple_versions
• What are the problems crashes hangs, or something else ?
  • Error Messages / Logs
    you mention shutting down, any more details or information & any error messages. (Also look at your Linux logs )
  • Other Causes
    I guess you have ruled out none Firefox problems including for instance overheating and faulty memory. (Is it only ever a problem when Firefox is running )
  • Crashes or Flash Hangs, please post the CrashIDs
    Troubleshoot Firefox crashes (closing or quitting unexpectedly)
    Send plugin crash reports to help Mozilla improve Firefox
• Turn on telemetry,
  it helps the developers, it generates complex data you may see and may find informative
  Share data with Mozilla to help improve Firefox
• Memory
  You are not going to be running low on memory, but note interactive reports may be seen at about:memory (key into addressbar)