Believe me, it's not the other software.

[wetworker]

Firefox 2.0.0.17 through 3.0.3 will not connect to internet, every version in between tried.

Running Vista Business and connecting via proxy server and been happily connected for weeks.
Was running 3.0.1 without issues. Upgraded to 3.0.2 and lost total internet connectivity. Uninstalled and rolled back to 3.0.1, still bad. Disabled Norton Internet Security and tried various iterations if 3.0.0/1/2 without success. After another uninstall and cleanup, I tried 3.0.3 without success.

Read a LOT of forum posts about this issue so 100% uninstalled ALL Norton products using their downloadable installer, they are gone, history, toast, nada.

Disabled WebRoot Spysweeper, uninstalled Firefox, ran 2 Registry cleaners and rebooted.
Downloaded and ran EnumProcess which says Vista's firewall is off and no other processes logged.
Installed Firefox 2.0.0.17 and still no internet connection after configuring it for the proxy server. Note that the RSS tab shows 'Live Bookmark loading...' nothing else. The 3.x.x versions would invariably state some form of connection error on the RSS feeds.

IE7, Opera and Chrome all working well, no internet or network problems at all. I can access my clients ftp site in Europe (I am in Vietnam) OK.

I did note that on the original upgrade from (last working) 3.0.1 to (first dead) 3.0.2 there was a prompt about an 'incremental upgrade' not being 'verified' or similar and the updater went for a complete download. This complete download was interrupted by some reset on the server and had to be repeated manually before installing.

No extensions or plugins as each Firefox uninstall I select to delete ALL the stuff (plus the registry hosedown).
Plugins installed:

[wetworker]

Just like to add that I posted this a week ago on the regular support.mozilla.com repository and so far NO response.

[LIMPET235]

Just trying something here, but have you tried installing Firefox in a new folder named, say, "Firefox 3" or sim?
Has worked before.
> http://www.mozilla.com/en-US/
Are you re-naming/deleting the Profile folder as well?
> http://kb.mozillazine.org/Profile_folder_-_Firefox
NB....The "Application Data", XP..("Appdata" in Vista) folder is a hidden folder;
To show hidden folders, open Windows Explorer and choose, Tools..(Organise) > Folder Options..(Folder & Search Options > Folder Options) > View (tab) > "Show hidden files and folders".

[teoli2003]

Try with a new profile. If not enough, uninstall Firefox and reinstall it in another folder.

[wetworker]

Yes, I am deleting everything Mozilla and Firefox related, which includes the Profile directory, each time as I learned from a small problem about a year ago that the Firefox uninstaller is... shall we say basic? In that instance I websearched and found detailed registry editing details that resolved that problem where reinstalls over the top of existing installations and uninstalls followed by reinstalls didn't fix it.

I did note that the latest attempt installing an EnglishUK download versus the usual EnglishUS version (clutching at straws here), it somehow picked up the proxy server settings without being told so that short prompt 'A little housework' when launching an installation probably means that the installer seeks and finds stuff that is still left behind after uninstall and registry cleanups.

But, the idea of installing in a completely different folder had crossed my mind so tomorrow I will try that.