It seems there is some external app blocking TB or FF from closing properly. Try running Windows in safe mode to test the effect of bypassing startup apps such as security/antivirus.

Remove the profile lock from both TB and FF in case it has been created:

http://kb.mozillazine.org/Profile_in_use#Remove_the_profile_lock_file

Thanks for the reply.

I just started putting stuff on this recently built PC. So far only have FF, TB and MS Works which I just installed last night. The only security/antivirus that's on the PC is Defender that came with Windows 10.

I noticed a day or 2 ago there were two Windows updates waiting to be installed & just installed them now. One was for Defender but don't recall what the other was. I thought they'd show up in "Installed Updates" but they don't. Could having Windows security not to date (until now) caused the problem?

I'll delete 'parent.lock'. Since the profiles were copied from my old Win7 PC why would the 'parent.lock' show up as a problem now?

Next time there's a problem I'll run Windows in safe mode.

Just the same, I would add the TB profile folder as an Exclusion in Defender settings, which is standard for any antivirus.

Depending on how the profile was transferred from the old PC to the new, the issue might be related. The best method is to create a new profile with TB 91 on the new PC and transfer data from the old to the new incrementally, especially if the old PC's TB version was 78 or earlier.

TB 78.14.0 is on both the old & new PCs. I figured might be better to use the same version on both in order to eliminate any variables during the transfer process & then update the new PC.

I copied each profile from the old PC to an EHD & then to the new PC.

I created a new Profile folder on the new PC’s D: storage drive & then copied each profile to that folder.

Then opened TB which is on the C: drive and created a new profile & chose the folder where it pointed to on the D: drive. Did this for each of the profiles. I did not copy the default profiles & let TB and FF create their own default profiles which stayed on the C: drive.

I’ve been using TB and FF throughout the day to make everything is working OK before I install more programs. Everything works great until it doesn’t.

I think you did everything correctly to minimize errors, but the only change I would make is to let TB and FF create their default profiles on C:, then delete the contents of those profile folders (leaving the folders defined as is) and copy in the contents of the profile folders from the old PC. That would test whether relocating the profiles to D:, which you did properly. is problematic in TB 91.

I came home & my wife was on the PC staring a big white screen that in the upper left corner said Thunderbird running but not responding. I could not close out by clicking on the "X" or using Task Manager.

I opened FF and it opened into a big white screen that said FF running but not responding. I could not close out of that either.

I could not power off via Windows & had to manually turn off the PC's power. There was no way to enter Safe Mode.

I'll try it with profiles on the C: drive and see what happens.

Could those default profiles that are on the C: drive be causing a problem? IOW profiles.ini points to some profiles on the C: drive and some on the D: drive.

I don't know if the presence of profiles on the C and D drives causes the problem. If you rename profiles.ini to profiles.ini.bak, a new one will be created when TB restarts.

I just renamed profiles.ini. When opening TB it wants to setup & configure an account, which I don't want to do. I'm not sure what I expected would happen when profiles.ini would be recreated, but was thinking more along the lines of re-entering paths to the existing profiles.

I'll move a couple profiles to the C: drive & see what happens. Should I delete the default and the default-release profiles?

Just let TB create an empty profile on C: and use the instructions above to delete the contents and copy in the contents of the old profile.

So far - The couple profiles I've moved to the C: have been working OK. But there have been 3 "not responding" problems with 2 profiles on the D: drive.

I looked in Event Viewer and there are entries listed there at the same time the last problem occurred. How do you interpret the data to find out what the problem is?

You can post some of the Event Viewer here if you like, but I think the problem is that TB doesn't work smoothly with profiles not on the installation (C:) drive. It's possible to keep the profile on C: but move the mail storage to another drive, since it takes the most space in a profile:

http://kb.mozillazine.org/Moving_your_mail_storage_location_(Thunderbird)

The TB profiles that were moved to the C : drive have been trouble free.

I saw something that said there should not be a profiles.ini file on the D: drive. I did put a copy of the old file there for reference & didn’t think it would be a problem. IOW why would TB even look there for it. Anyway I renamed it and so far there are no problems with the D: drive profiles. Hopefully that solved the problem.

But Firefox has now had 2 occurrences of “running but not responding”.

The only time I had a problem before with FF was trying to run it when TB was locked up. This caused FF to lockup & I presumed one was affecting the other.

But now FF just locked up by itself. IOW I could open TB and it worked. In this case one did not affect the other. There are 2 FF profiles on the D: drive and and backup copy of the old profiles.ini which has been renamed. Not sure why FF is now acting up, but cannot Restart or Shut down when that happens & have to power off the PC.

If FF acts up again I'll move its profile to the C: drive & see what happens.

I think TB and FF have the same requirements for profiles, so it's probably necessary to keep the FF profile on C:, which shouldn't be a problem since browser profiles are usually much smaller.

I put the FF profiles on the C: drive because it did act up again. Now it's self contained on one drive.

TB was working great since I renamed the old profile.ini that was on the D: drive, and all the profiles are back on the D: drive.

But now I opened TB & it just froze & said "not responding". I tried to use taskkill to kill the PID that displayed in Task Manager, but this said it couldn't kill it because it was not running.

I deleted the re-named profiles.ini that was on the D: drive just to make sure it was not in the picture. We'll see what happens.

Everything was working great last night, this morning & this afternoon. That's about 24 hours of success.

But then FF froze when opening. Just a plain white screen & no mention if it was running or not responding. Nothing.

Went into Task Manager & there 4 instances of FF running. I was able to end 2 of them but the other 2 said "The operation could not be completed" and "Access is denied".

Tried to use taskkill and kill the PIDs of the 2 remaining running FFs. But it said could not be done and they were not running. Task Manager says they're running, taskkill says they're not. Had to power off the PC.

A couple hours later TB opened to a white screen & froze & the message in the upper left corner said it was not responding. And once again I could not end it and had to power off the PC.

FF and it's profiles are all on the C: drive which I thought solved the problem but obviously not. Since the D: drive is not used for FF that should help eliminate problem areas.

Any suggestions where to go from here? Should I also post this in the FF forums?

An issue that comes and goes is hard to diagnose. You've already tested in Windows safe mode, but I wonder if there is some other process besides antivirus that could be interfering periodically, such as an online backup app.

Wouldn't hurt to post in the FF forum; include a link to this topic.

Here's the short version - Two weeks ago I had a problem copying files from an EHD to the D: drive because the PC said the D: drive didn’t exist.

I reseated the M.2 D: drive & got a message when booting up that there was a problem & it was being fixed. The D drive then showed up.

Two days later the D drive did not show up when powering up the PC. Rebooted the PC & got a message there was a problem that was being repaired & to note the error code. It happened so fast I could not write down the error. But everything worked, or so I thought. FF & TB were installed after that time & had problems.

Four days ago I ran sfc /scannow & it supposedly fixed/replaced some files. I looked at the log file but can’t find what it fixed. But TB & FF having been working just fine since then.

I spoke too soon. Today TB opened & froze & "not responding". I'm going to format both drives & restore an image on the C: drive.

I did restore an image about 24 hours ago & TB has worked OK until now. It just opened to a blank screen & "not responding".

Every time I walk by the PC I check email & probably opened TB 25-30 times without a problem. If a TB file was corrupt or missing then how could the program work all day?

Could there be something in Event Viewer or a log that would indicate a problem? While in Task Manager I created a dump file before powering off the PC. Might that contain information about the problem?

Thanks for your help.

I replaced the 1TB M.2 SSD D: drive with a 1TB spinner HDD that I was originally going to use. That was 8 days ago & no problems since.

I'm not sure why would would make a difference because at one point the Firefox profiles were on the C: drive and FF still had a problem. That being said, the earliest problem I had was copying files from an EHD to the D drive which did appear in File Explorer. But the error message indicated there was no D drive. After rebooting the PC the D drive did NOT appear in File Explorer. Another re-boot got it to appear but Disk Management then showed it had an extra 2MB partition off to the right side, which wasn't there before.

It's working & will leave it alone for now.