This is a problem I used to have with Firefox updates failing when I was running as a Limited User in Windows XP.
Here are the steps to fix the problem:
- Close all running instances of Firefox.
- Open an Administrator command prompt by right-clicking on a Command Prompt icon, choose Run As... and enter the credentials of a user with administrator rights.
- Launch Process Monitor from the administrator command prompt by typing the full path to the executable (wherever you installed it). For example: c:\apps\procmon.exe (tab completion can be very helpful for this step).
- Within Process Monitor, turn off "Show Registry Activity" and "Show File System Activity" from the toolbar. Only "Show Process and Thread Activity should be enabled". This step is not absolutely necessary, but it will eliminate a lot of extra noise.
- Start Firefox, and click through the "Software Update Failed" dialog until the browser opens.
- Switch back to Process Monitor and press CTRL-E or the click the toolbar button to stop capturing events. Close any Firefox windows that might be open.
- Scroll through the list of processes and double-click on the first instance of "updater.exe" (it should have the value "Process Start" in the Operation column). Switch to the Process tab of the Event Properties window that opens.
- Select the entire contents of the "Command Line:" textbox and copy it (CTRL-C or right-click, Copy). It should look something like this (all one line): "C:\Documents and Settings\Josh\Local Settings\Application Data\Mozilla\Firefox\Mozilla Firefox\updates\0\updater.exe" "C:\Documents and Settings\Josh\Local Settings\Application Data\Mozilla\Firefox\Mozilla Firefox\updates\0" "3824" "C:\Program Files\Mozilla Firefox" "C:\Program Files\Mozilla Firefox\firefox.exe"
- Switch back to the administrator command prompt and right-click, Paste to paste the command-line. Press Enter.
- You should see a dialog indicating that Firefox is updating. Close the browser that opens since it is still running as the administrator.
- Now open Firefox normally. It should start up without the annoying error message.
Source: Flimflan.com