User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1) Gecko/20061010 Firefox/2.0 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1) Gecko/20061010 Firefox/2.0 This evening, while I was visiting my uncle's house, I updated their copy of Firefox from 1.5.0.8 to 2.0. I downloaded the 2.0 installer, closed Firefox, and ran the installer. The results were disastrous - when Firefox started up again, it malfunctioned noticeably in a number of ways. - The spell checker did not run (e.g., the word fasf was not underlined) - There were no search engines listed in the search engine box - It began with a single window, as expected. I opened a new tab with control+T. There were then two tabs; let's call them Tab 1 and Tab 2. When I opened it, Tab 2 did not get the focus - it opened in the background. When I switched to Tab 2 by clicking on it, its location bar contained the address that Tab 1 was currently displaying. When I typed in a new address, Firefox opened that address in Tab 1, not Tab 2 as it should have. Man, that was really weird. I concluded at this point that something had gone horribly wrong, so I decided to uninstall Firefox, delete the profile, and install fresh. This I did. The problems re-occurred. Finally, I figured out what was going wrong: this is a family computer, having four accounts, one for each family member. I was logged in on my cousin's account, but my Uncle was currently logged in also, and had left a copy of Firefox 1.5.0.8 running in his account. That would probably account for the above-mentioned bizarre behavior. And plenty more besides! When my uncle rebooted a couple of hours later, XP died just before reaching the "Log In" screen. Blue screen -- not a blue screen of death, just a blank blue screen with no words, no mouse cursor, nothing. That's a major problem. I had gone home by that point, and had to do support over the phone - we rebooted that sucker like ten times, I did some research, and we did in fact manage to get it up on its feet again after an hour and a half of attempts. (The solution involved running chkdsk /r, which we couldn't do until we managed to coax it into a command prompt by sheer luck. While I was doing research, Uncle didn't touch it for fear of causing more problems, and it eventually finished booting into the command prompt we had selected on the previous attempt to boot. Apparently the hangup had to do with the hard drive.) So: I was able to recover from this fault. But I bet you 99% of the computer users in the world would NOT be able to do so. Furthermore, rendering the host operating system unbootable is just generally a bad thing. If I recall correctly, the Firefox installer checks for currently active Firefox processes and refuses to proceed until the older version of Firefox is closed. However, apparently it doesn't check to see whether there are Firefox processes running under a different user name in an XP environment. Although this state of affairs is definitely uncommon, the potential consequences are so severe that it really needs to be fixed. The new Windows installer is written in NSIS, right? I've glanced at the documentation for that in the past, but never used it for anything. Is it capable of checking processes started by other users? 'Cause that's what it needs to do. Reproducible: Didn't try Steps to Reproduce: 1. You'd have to be insane to try and reproduce this unless you were using a sandbox machine.

Excellent diagnosis - it took us a while to figure out the cause. *** This bug has been marked as a duplicate of 357922 ***