What about looking in Task Manager->Processes for firefox.exe and killing it by pressing button "End Process"?

There should be at least two processes, I assume: one visible and trying to update and one invisible preventing him. Kill them all, and then start Firefox and try to update again.

Does it help you?

No 'Wikiwide'... That's the problem...

The Task manager keeps on telling me (us) that there are no processes running and Firefox is comming up over and over again with the same message (see discription above).

It is not possible to use 'Firefox' anymore...

Find Firefox profile folder

%APPDATA%\Mozilla\Firefox\Profiles\xxxxxxxx.default\

In this folder a running Firefox puts file "parent.lock". Mere presence of this file will put Firefox into illusion that another Firefox is already running. So delete this file.

Usually Firefox deletes the file itself. But if the Firefox exited in unusual way (was killed/crashed), it may forget to delete this file. So delete it manually, and try again.

Does it help you?

"Firefox is already running but is not responding" error - How to fix

See http://kb.mozillazine.org/Software_Update (Software Update not working properly)
Remove the files in the updates and updates\0 folder:

XP:
C:\Documents and Settings\<user>\Local Settings\Application Data\Mozilla\Firefox\Mozilla Firefox\updates
%USERPROFILE%\Local Settings\Application Data\Mozilla\Firefox\Mozilla Firefox\updates
C:\Program Files\Mozilla Firefox\updates
.....
Vista/Windows7:
C:\Users\<user>\AppData\Local\Mozilla\Firefox\Mozilla Firefox\updates
%LOCALAPPDATA%\Mozilla\Firefox\Mozilla Firefox\updates
C:\Users\<user>\AppData\Local\VirtualStore\Program Files\Mozilla Firefox\updates

I tried to find %APPDATA%\Mozilla\Firefox\Profiles\xxxxxxxx.default\ in order to delete the "parent.lock" but my search of C drive found no results. How can I find this folder?

I tried to find %APPDATA%\Mozilla\Firefox\Profiles\xxxxxxxx.default\ in order to delete the "parent.lock" but my search of C drive found no results. How do I find this folder?

I also found the file SOURCE DIRECTORY C:\Users\Eric Shrode\AppData\Local\Mozilla\Firefox\Mozilla Firefox\updates\0 which had a lot of files but no way to delete them.

I do know that if I just click on cancel the failed update then I can still get to Firefox but it's a pain. Perhaps time to go back to MS Explorer

You can either delete the full update or update\0 folder to remove the already downloaded update or you can try to run Firefox once as Administrator to see if that allows the updater to apply the update.

If you fail to update Firefox then make sure that the updates folder is empty and then download a full version of the Firefox installer (http://www.mozilla.com/firefox/all.html) to update to the current Firefox release.

I must admit I only use Windows 7 when helping one of my sons... I'm sticking with XP for a while longer <VBG>. Using the XP routine-The parentlock file is found by opening C:\Documents and Settings\*whatever you named yourself as the administrator\Application Data\Mozilla\Firefox\Profiles\*a folder named something like ZX90oppp\. The parentlock file is not in the sub-folders, but in the main Profile files. BTW, be sure Firefox is indeed closed before doing this. Otherwise, you'll be told "a program is using this file and you cannot delete it." Hope this helps....

I had this problem too. I searched for a solution and this is what worked..

I have two users accounts on my computer and the other user had firefox open.

So once we swapped users, closed that firefox window, came back to my user account then the update ran without any problem at all.

I had the same problem. Just right click the firefox icon and select "run as administrator", the update works then.