Over the past couple weeks I've been running into restart messages from Firefox that say "Your computer must be restarted to complete a previous upgrade of Firefox. Do you want to reboot now?". (Attached an image as well.)
I'm on the most recent version of Firefox (15.0.1) and these messages seem to start randomly during the day. For example, two days ago I had an upgrade to Firefox, which I applied, and then restarted the browser. Everything was working fine for a few hours, and suddenly I received the restart message again. Sometimes it happens on a day (such as today) when no updates happen.
The message pops up whenever I click on an external link that would normally open in Firefox, my default browser. Instead of opening the link in a new tab, the message pops up and won't allow the link to open. However, I can copy the link location and paste it into a new browser tab and it works fine.
Last week I followed the steps on this page: http://support.mozilla.org/en-US/questions/757325
and I also had to reinstall Firefox. The messages went away for a day or so and then came back.
My OS is Windows XP Pro version 5.1.2600. I use Thunderbird, which is also Mozilla.
I'm hoping someone has some insight as to why this could be happening or how to fix it. Let me know if there's more information I can provide or anything I should try.