You have tried the obvious troubleshooting steps. I know from recent experience that even running Memest overnight may miss memory related issues that disappear once the RAM is changed.

Just a hunch but maybe there is some regression in Firefox, on Linux/Mac that produces multiple & various Crash Signatures. Any such regression would be hard to pickup from crash Stats.

No guarantee this will be any help at all; and it is not a cure, but may be a temporary workaround, enabling you to get Firefox running again Crash free while you investigate further. May also prove; or otherwise; that the RAM is OK

Try installing Mozilla ESR 38 as an additional Firefox browser.

• See & obtain download from (Note the 38/45 selector option)
  https://www.mozilla.org/firefox/organizations/
• Follow Install Firefox on Linux modified as necessary for ESR

Forum notes

• Crash Reports
  1. bp-bab24358-80d4-4b70-a7aa-bbec02160323
  2. bp-c1a4b3be-464b-43e5-9a31-e3bab2160323
  3. bp-9da6d876-66d9-400f-a8db-8560a2160323
  4. bp-5aca0ccc-fb90-4bb8-bdd8-a0ada2160323
  5. bp-2262d18b-47c3-4faf-9edf-207512160323
• Crash Signatures
  1. Signature: js::ConstraintTypeSet::sweep
  2. Signature: DispatchToTracer<T>
  3. Signature: js::GCMarker::markAndScan<T </li>
  4. Signature: nsRefPtrHashtable<T>::Get | mozilla::Preferences::RegisterCallback
  5. Signature: DoMarking<T>

• Related bugs (My comments)
  • (T.bird !) Bug 1174997 - Crash in js::ConstraintTypeSet::sweep
  • (I have cross linked to this thread) Bug 1220385 - crash in js::ConstraintTypeSet::sweep
  • Bug 1191503 - Crash [@ DispatchToTracer<T>(JSTracer*, JSString**, char const*)]

John99 said

Try installing Mozilla ESR 38 as an additional Firefox browser.

• See & obtain download from (Note the 38/45 selector option)
  https://www.mozilla.org/firefox/organizations/
• Follow Install Firefox on Linux modified as necessary for ESR

This worked for me, thank you!

That's great.

It is however only a temporary solution. Besides the ESR not being officially supported for individual use it is transitioning to the ESR Fx45 & that probably will crash.

Of course as you reconfigure & customise the new install that may also start crashing. That would be bad news for you, but at least may help shed light on reason or contributory factors for the crashes, so please let us know if you do see crashes on ESR38.

Unless you manage to spot any patterns or discover "Steps To Reproduce" the crashes its probably now a case of watch and wait and hope that someone does find a fix for these issues.

Update. At least one of these crashes {^{Bug 1220385 - crash in js::ConstraintTypeSet::sweep} ) is apparently fixed in Firefox Beta, but not likely to be fixed in the initial Fx49 which is out soon. Hopefully Firefox 50 will be fixed.