Upgrading to latest Fx version

Question

When it comes to installing new versions of software whose current version I can continue to use without problems, I am what might be called a "last adapter." Perhaps because I've been "hurt" by buggy new versions in the past, perhaps because I'm getting old and lazy about learning new interfaces and features--whatever the reason, I'm slow to upgrade unless I'm faced with some obvious danger. So I've stuck with Firefox 3.6.x after version 4 came out, thinking I would wait until something like a version 4.2 arrived. While waiting, much to my surprise version 5 showed up!
Finally, today, after backing up my entire hard drive and updating my system software and my plug-ins, I was ready to take the plunge. For some reason, however, although I had spent the past several weeks turning down many repeated automatic invitations from Firefox to update to version 4 (but eventually accepting only security updates for versions up to 3.6.19), now, when I clicked "Check for Updates," I was told that none were available.
It occurs to me that some fuction may have been changed on the Firefox servers after one or more security upgrades had been made available for holdouts like me: maybe the "Check for Updates" function was limited to 3.6.x versions? The message I got today would make sense, then, since I have the latest version (3.6.19) installed. But this is only a guess.
At any rate, I decided to directly download version 5, which was not difficult to find. Opening the file, however, when I dragged the installer's Firefox app icon to the aliased icon of my app folder, I got this unexpected message: "A newer item named 'Firefox.app' already exists in this location. Do you want to replace it with the older one you're moving?"
Of course I immediately double-checked both the new version (newly downloaded file "Firefox 5.0.1.dmg") and the old installed version (clearly 3.6.19).
I should probably just ignore this warning message and click on "Replace," but by now I've got an "upgrade headache." It's a small pain compared to some others I've had in past years with different software, but it's a pain nonetheless.
What in the world is going on?
Basics about my system (in case it's relevant):
Mac Snow Leopard (totally up-to-date, including plug-ins)
All cookies (including Flash), caches, browsing history completely deleted immediately before today's update attempt.

Answer 1

The default of the pref network.http.max-connections has been increased from 30 to 256 in Firefox 6+ versions.
Try to decrease the value of the pref <b>network.http.max-connections</b> from 255 to a setting like 30 as used in Firefox 3 versions.
*https://support.mozilla.com/kb/Firefox+never+finishes+loading+certain+websites
A possible cause is security software (firewall) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.
Remove all rules for Firefox from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.
See:
*https://support.mozilla.com/kb/Server+not+found
*https://support.mozilla.com/kb/Firewalls