Update.

After many logoffs, restarts and switching user from the temporary profile and the second user account, it randomly let me back in to my original profile again.

I literally did nothing to allow me access to it other than many of those attempts.

As soon as I was in my original account again, I immediately went to the control panel -> uninstall a program and verified, same as last time, that it listed two instances of FF (recall that it did NOT after I upgraded before the first restart and getting the temp profile). I opened up FF, 16.0.1, and downloaded it again from http://www.mozilla.org/products/download.html?product=firefox-16.0.1&os=win&lang=en-US

Installed that, even though it was already successfully installed according to FF. And just like last time, that removed the earlier instance of FF, 15.0.1, and all is back to normal. Verified by restarting multiple times and no longer getting a temp profile (exactly like last time which lasted for about three weeks until the 16.0.1 upgrade).

This never happened until 15.0.1 and now 2 for 2 with 16.0.1. What is going on that would yield a successful upgrade yet on Windows 7 first restart after is causing it to kick to a temporary profile (yet also fixed, if one gets lucky enough to get back their profile, re-installing it over fixes it until the next upgrade?)? Some file not being created/deleted on reboot that is confusing Windows when trying to load the user profile?

I'm willing to copy over my W7 user profile to a flash drive and Fedex it to the FF team if one can fix this. It is the most basic software setup that I can't imagine others aren't experiencing the same issues.

Thank you so much for posting the problem. Last month was the first time I have ever had this problem. I finally just made a new user profile and abandoned, but not deleted the old profile. So, last night I let the updater install Firefox 16.0.1 and lo and behold my "new" profile would not work on boot this morning, but the abandoned one was working! SO, as per the above post, I uninstalled 2 versions of FF in my control panel. I downloaded 16.0.1 as a new install and then rebooted. Now both profiles work again. There must be something wrong in the updater program, corrupt user profiles are a real pain!

Glad you got it fixed.

Unfortunately, if my situation is common, it looks like it will just happen again whenever the next updated release comes until it is fixed.

Note also, not sure if it makes it any easier, that I did not have to uninstall anything either time. I just re-installed FF from the site over the previous install which then automatically both fixed the issue and the two instances of FF versions listed in the control panel. No loss of any Windows user profile data or FF settings.

I hope this gets fixed before the next release as I have no idea how it allows one back into that corrupted user profile when it happens other than blind luck after many, many attempts.

16.0.2 Update.

I had put the Firefox updates setting to check for updates but let me choose when to install them. When I received the new update notice I selected "ask me later" and this time instead went to the site to download it.

http://www.mozilla.org/products/download.html?product=firefox-16.0.2&os=win&lang=en-US

Saved the file and ran that rather than through the updater and had no issues whatsoever. I have restarted a couple of times and all is good.

I'll continue to handle it this way from now on unless/until Firefox states this issue has been fixed in a future update. Glad this bypass method works as I was one more time dealing with this away from permanently switching browsers.

Hope this works for everyone else experiencing the same issues when updating to new versions since 15.0.1.