Container started as a testpilot experiment and was added to Firefox 57.

• https://testpilot.firefox.com/experiments/containers
• https://wiki.mozilla.org/Security/Contextual_Identity_Project/Containers

Were you still using the same profile or was a new profile created by using refresh feature in Firefox?

You can check if you have an "Old Firefox Data" folder on the desktop in case the Refresh feature in Firefox has been used and a new profile has been created.

• https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems

I didn't use Refresh feature (I never do as it resets my preferences) and I have no "Old Firefox data" folder on the desktop. Ignoring the new "tabs containers" was being developped I didn't try to do anything / testing beta or whatever related to it, although some weeks ago I intalled the "Tree Style Tab" extension. The profile is still the same and only (beside the one used by FF38 I seldomly use). Profiles.ini wasn't changed as well. I forgot to say that upon the startup that showed the issue, I got the usual tab we get on new install. And in the profile I found my 900kB logins.json renamed to logins.json.corrupt beside a new 700kB logins.json. as well as a new Invalidprefs.js I never noticed before. Digging at the moment to redact this answer, I also find a new extension-settings.json.corrupt. So far all if restored now regards to FF Sync, but the question remains about prereqs because my AMD A8 Ubuntu14 64bits doesn't show the Tabs Containers feature neither in File menu item not the so called Hamburger menu, although loading "about:preferences#containers" shows fine the graphical settings subsection. Anything special with AMD APU's ?....

... Okay, don't bother, I think I understand : Containers Tab is still beta and as so is not yet spread in the wild : I discover an option in General preferences a grayed checked "Enable contextual Tabs" option showing Tree Style Tab requires the feature : here is the prereq, i.e. on the opposite side where I thought it lacked :-)

On the A8 machine, no option visible as privacy.userContext.ui.enabled=false

Should I have to say I had a huge amount of tabs (mainly unloaded). Also when the issue happened, the side panel was showing History, not tabs (although I can easily figure the extension was running to react on F1(what BTW I don't like as F1 would remain standard help Key - this is not a mozilla issue, instead the TST extension dev one))

Files with corrupt in their names are created when something is wrong with the main file that is beyond repair. You will have to check each file to see if you can identify the corruption and try to repair it on a copy of the corrupted file or what I would try in a new separate profile.

If you do not switch update channel or downgrade to an older version then you wouldn't suffer of file corruption unless something was already wrong or there is a permission issue. I always install Firefox in a location with root access (/usr/local/mozilla/), so I can control Firefox updates myself using sudo. A forced close can cause issues when file writing is interrupted, but then I don't think that that many files would be corrupted at the same time.

Note that Firefox 58 uses SQLite databases key4.db and cert9.db, but will fallback to key3.db and cert8.db when you remove the newer version.