This sounds identical to the problem I've been having, except I'm running Win 7. dancer1

Also see the following thread: https://support.mozilla.com/en-US/questions/900136#answer-281339

With a minimum of 8 users (who've bothered to post) experiencing an identical problem, perhaps Mozilla should look into this.

This sounds like the problem i am having also. im running win xp 64 bit and when i try to launch firefox ver 8.0.1 it opens the window afew a pause and you see that its connecting 2 blank tabs are open and it just hangs there it will not connect and you have to kill the app in task manager it says its not responding. i have un installed FF and all add ons and tried a fresh re install but it does the same thing. ive ran the latest version of avast anti virus and detected no problems. IE seems to work fine but i hate IE. this problem seems to have started last night i was prompted to update adobe flash plugin. since then FF has been DOA. i hope someone finds a fix for this.

Mozilla, I am waiting for a fix, I want my 7.0.1 version to work again, your version 8.0.1 is not good, you cannot expect to disable all of our stuff....are you kidding me!?! I'll stay in Safari, not to worry, uninstalled Chrome when they got stupid and never use IE because it's always been stupid....Safari must be the way to go!

Me, too!

The Mozilla servers experienced a major outage recently and so if you have tried to download Firefox, or have add-ons set to update automatically, or are using Sync, you may have been experiencing server time-outs.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode (hold down the SHIFT key when starting Firefox) to check if one of the extensions or if hardware acceleration is causing the problem and to make sure you are using the default theme:

     Firefox (Tools) -> Add-ons -> Appearance

Don't make any changes on the Safe mode start window.

     https://support.mozilla.com/kb/Safe+Mode 

See also the help article:

     Troubleshooting extensions and themes

Also make sure to update your plug-ins (Java, Flash, etc.)

     https://www.mozilla.org/en-US/plugincheck/

The following help articles address crashes in Firefox:

• Firefox will not start

• Firefox crashes

• Firefox crashes when you open it

• Firefox is already running but is not responding

• High memory usage

You can also search for similar help articles

If you have to re-install, do a clean installation:

1. download Firefox and save installation file,
2. uninstall Firefox,
3. delete the Firefox program files folder, (important)
4. reboot
5. re-install with administrator privileges. (important)

Firefox hangs the same way in safe mode.

There is no such thing as a Firefox program folder on a Mac, nor is there an "uninstall" to do, so these directions are not relevant to a Mac user.

The problem remains.

On Mac OS X, a crash can be caused by a preference file being damaged. Quit Firefox, then go to your user Library -> Preferences, find the file "org.mozilla.firefox.plist" and move it temporarily to another place, like your desktop. Restart Firefox and a new .plist file will generate. If that works, you can delete the .plist file you moved. See:

http://www.macfixit.com/article.php?story=20060606082246983

That was one of the first things I tried. That's not it--still hanging on launch.

Mac OS X Lion FF 8.01

It's very strange. When FF hangs I click on the yellow dot to minimize the FF window into the dock. After clicking it on the dock and restoring it FF works again.

Check to see that disk permissions are intact on all plug-ins in both the system-wide /Library/Internet Plug-Ins/ and ~/Library/Internet Plug-Ins/ folders. Move system-wide plugins into the Disabled Plug-Ins folder, and clear the personal ones.

Then delete org.mozilla.firefox.plist again, back up and delete the Application Support/Profile(s), and delete the Firefox folder in ~/Library/Caches.

Then run the Disk permissions fix, and restart and do a clean install.

Please post back your result.

What are the permissions supposed to be?

It's not possible to click on minimize while it is hanging.

If you run disk repair from the installation dvd, the report will show you where permissions differ and what they should be.

An example of some permissions reporting that Apple tells you you can ignore, is at:

     https://support.apple.com/kb/ts1448

however, since you are having issues that are likely related to the Firefox install and plug-ins, and probably aliases, it would be best to correct permissions issues to rule that out as a part of the problem. Also get rid of any aliases related to Firefox or its plug-ins.

I have been traveling and don't have the install CD with me to restore permissions.

I downloaded Firefox 9.0.1 and now the hanging is on the "Checking Plugins for Compatibility" dialog box.

Does this provide a clue to anyone?

I have been using version 3 for years, as every time I tried an update, it would hang. Same with 9. So I always had to go back and reinstall 3, where everything would be fine. 9 works on my laptop with Vista, and the new feature I wanted was the sync, to be able to sync bookmarks. Love that idea. But on my desktop with XP, could not for the life of me get Firefox to work with any version past 3.

Here's the solution that worked for me:

   opened the version that worked, and saved bookmarks to USB drive. That's the main thing I wanted in the new version.
   uninstalled FF
   manually deleted all files in FF and Mozilla folders on the hard drive, including any folder named "mozilla" or "firefox"
   edited the registry (read about how to do this properly elsewhere) and manually did a search for and removed every single instance of "mozilla" and "firefox" that existed on the computer. Made sure I did search from the top of the registry tree
   rebooted
   installed firefox 9
   imported bookmarks from USB drive 

all works fine now! Years of upgrades not working, and a registry clean did the job.