some months ago I was asked to look at forcing the Proxy settings for Firefox through GPO (Group Policy), to begin with I wasn't too sure it if was possible or not but turned out that it was, I will put something up on how to lock down Firefox through GPO later.
Any way I just thought if I remove the policies I'd put in place that would disable it, but no! I disabled the policies and scripts and no joy we were still getting the proxy settings forced and could not change them.
In order to force the settings you need to run a computer start up script (at computer start up funnily enough!!). So I had a look at the script and noticed that there were several entries made into the windows registry, specifically in to HKLM\Software\Policies\Firefox so I had a look in there and deleted everything in there (as it contained several settings for the proxy and default home page) re-started Firefox and no joy, so I restarted my PC, still no joy.
I then noticed in the firefox_startup.vbs file that there was a line:
FirefoxPrefsFile = EnVar("ProgramFiles") & "\Mozilla Firefox\defaults\autoconfig\prefcalls.js"
So I wen and had a look in C:\Program Files\Mozilla Firefox\defaults\autoconfig and saw that there was a file called prefcalls.js. I opened that file up and noticed that it had a lot of "lockedout" settings applied that related to our proxy server address and port. so I deleted all those lines and then restarted Firefox and it worked. I could now change all my proxy settings as and when I wanted to.
