I'll vouch for Switchproxy (https://addons.mozilla.org/firefox/125/) as well. I use it to switch between three different proxies at work, and none at home.. makes the change a two-click process, and is yet another reason why I can't use that other browser.
I don't know how Squid would go at detecting upstream proxies. I'm sure it would, eventually, but it would probably talk longer to figure out what was going on than two clicks to change your proxy settings would take... As for saving sessions and using tabs - just grab Alpha 3 of firefox 2 and it's all built in :) You could grab the beta as well, but my experience so far hasn't been great - it's crashing about twice a day. Of course, built in session restoration means that crashing is a pretty trivial event, but still... -- There is nothing more worthy of contempt than a man who quotes himself - Zhasper, 2004 -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
