I am pretty sure - based on my own experience - it has to do with the newly introduced "Firefox health report".

It happens to me every time I close the Fx 21 and I am slowly getting used to it.

Regards

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Restarted Firefox in safe mode, the prompt didn't appear. Then started Firefox again in regular mode and it didn't appear either.

Guess that solved it.

Thanks!

Then started Firefox again in regular mode and it didn't appear either.

- not in my case. After the safe mode (no prompt) the prompt reappeared again on exiting the next (normal mode) firefox session. This indicated one of active add-ons as the cause.

After I deactivated the Firefox OS Simulator, the command prompts on Firefox exit stopped. Check your Tools > Add-ons, to see if this is the reason for your continuing problem.

PS: ... so, btw, it was NOT the "Firefox health report".

Hey smo,

I do have the FOS simulator, but I had it deactivated at the time the prompt appeared. So might be a different cause for me, I'll check what activating it does for me.

Kind regards

The simulator does bring up a prompt. But this one seems related to extensions, rather than the one I had about the browser profile.

So it's a different cause, but I haven't come across the profile related prompt since I tried safe mode.