I was a major fan of Firefox since shortly after it started, and it was my primary browser for years. Then I upgraded from v.3 to v.3.5 somewhere around last June and had nothing but trouble after that. Searching forums and websites convinced me that there were plenty of other people having the same difficulties. I finally couldn't put up with all the crashes and switched to Google Chrome, which has been my primary browser for a couple months now.
The main trouble was instability, crashes, and slow behavior. I wrote a couple blog entries about it, if you're interested in more details on the problems I (and others) had/have since 3.5 came out in June. Minor version upgrades since then have not eliminated any of my problems.
http://hdjones.wordpress.com/2009/10/10/firefox-you-should-be-embarrassed/
http://hdjones.wordpress.com/2009/11/02/another-firefox-update-same-old-shit/
Until now I was advising people to stick with Firefox v.3.0.14, but this month Mozilla will stop issuing security and stability updates for the older versions, so you run an increasing security risk if you don't upgrade.
I have no quarrel with Internet Explorer 8 except there aren't as many add-ons available as there are for Firefox. Many people say IE8 is slow to load (the program, not the pages), but I got rid of some of it's unneeded add-ons from the start-up and now it loads as fast as any other browser I have.
I don't think you can have 2 different versions installed simultaneously, but I'm not sure about that. Internet Explorer 6 is not a very secure version, and you will have a safer Internet experience if you upgrade to version 8, or even 7.
--Cystem
I am currently running Internet Explorer 6 and am thinking about uploading
IE 7 and/or IE 8.
I also am running Firefox 3.0 and am thinking about uploading Firefox 3.5.
Is it okay to upload the new browsers and keep the old ones? I hear many
people don't like IE 8 and I would like to keep IE 6.