Did you check for issues caused by other extensions?

If it works in Safe Mode and in normal mode with all extensions (Firefox/Tools > Add-ons > Extensions) disabled then try to find which extension is causing it by enabling one extension at a time until the problem reappears.

Close and restart Firefox after each change via "Firefox > Exit" (Windows: Firefox/File > Exit; Mac: Firefox > Quit Firefox; Linux: Firefox/File > Quit)

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

If you do not keep changes after a restart or otherwise have problems with preferences, see:

• http://kb.mozillazine.org/Preferences_not_saved

Delete a possible user.js file and numbered prefs-##.js files and rename (or delete) the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in the current Firefox release.

Cor-el - I just did a reset and did NOT re-install any add-ons dealing with proxies. But same symptoms. If I manually turn on a proxy, it works if I don't leave the tab I'm in. But if i go to another tab or start a new tab, the proxy is turned off goes back to "No proxy". What to do?

Is this happening in a clean profile without any extensions like QuickProxy installed?

Yes. The only one that might be new is "Disconnect Search". But it's not a proxy, is it?

FYI - My addons (which I've had for a long time) are No-Script AdBlock Plus Better Privacy Perspectives IE Tab 2 Disconnect (last two months) Cookies Manage + Bloody Vikings (almost never used) Email Link Xmarks Most recently - Disconnect Search

What do you think?

It's Discover Search. The problem goes away when Discover Search is disabled. Too bad - it's a good, useful app. May I ask you to contact them to ask them to clean it up?

And now I just installed QuickProxy, and it's working.

Thanks for reporting back on your findings.

Do you still have issues left?