Well it should be possible to fix that by turning off the new multi process feature of Firefox.

Normally the new feature is an advantage. The odd Gah message indicate that a tab has crashed but the browser itself should continue working as normal. I do not understand how you get such a crash from a blank tab.

Pre release versions of Firefox have easier methods of turning this feature off or adjusting its settings but for now: Disable multi-process tabs in Firefox by setting the related prefs to false on the about:config page.

browser.tabs.remote.autostart = false
browser.tabs.remote.autostart.2 = false 

• See also
  • http://www.ghacks.net/2016/07/22/multi-process-firefox/
  • Configuration Editor for Firefox

The tab crashes should be generating crash reports, can you try in Firefox's safe mode and with a blank startup tab and when it crashes visit about:crashes to obtain the CrashID for that tab crash and paste that crash ID in to your reply please.

• See Troubleshoot Firefox crashes (closing or quitting unexpectedly)

Even after Firefox has been installed and used does the crashing stop the first time you use Firefox in a new additional Firefox profile ? If so that indicates your wife's issue is due to some problem in the profile. Possibly comparing a new profile with a profile after closing down and restarting may throw some light on what is happening.

Thanks for the reply .. it seems to have fixed it. The setting "browser.tabs.remote.autostart.2" was set to true .. toggling it & restarting and FF is back to normal on repeated FF restarts. I even restored the old profile (and had to toggle the above setting off again) and that worked fine as well. So at least on that pc the multi-process feature causes FF to be essentially non-functional.

Prior to the fix opening FF resulting in a single tab with the Gah error. This was the case with both the original profile and also a brand new clean profile (I removed the original profile when I reinstalled FF). Opening another tab gave a blank tab but trying to go to any page (or even a local html file) gave the gah error.

The latest crash ID was: c5032d86-3aca-46c4-b416-a3c2ed6020c3

Re different profiles .. when it updated to the troublesome version with the original profile it gad'd on the next (and all subsequent) sessions after the successful update. After the next FF update it worked for the 1st session and then just Gah. I uninstalled and copied the old profile to a temp folder, then deleted the ..\users\..\firefox\ folder, not just the profile, but the entire mozilla folder, then reinstalled FF, so a completely new install & profile. Ran FF .. worked fine. Closed, ran again and it Gah'd. So with a clean profile, opening, visiting google, closing and re-running FF that was enough to corrupt something. Since the SAME profile worked fine with the latest portable version (just copied the entire contents of the original profile folder into the portable profile folder), that seems to suggest the original profile was not corrupted but the problem lies elsewhere.

Most likely the multi-process setting is clashing with something else on the pc .. but what would be the million $ question & a major pain to work out. No idea if it's an OS setting or another programme.

One more question .. any idea if future FF updates will toggle the b.t.r.a. setting back to true or will the false setting persist? FF updates have in the past sometimes changed non-standard config settings back to the default, othertimes not.

Thanks