I was on McAfee for a few years with no major problems. I recently changed to Norton and that effectively reinstalled firefox destroying existing profile and putting a norton toolbar on. Luckily things most things were recoverable.

So now I've had my rant lets think about your problem.

• what is giving the 404 error ? ie which address are you trying to connect to
• sorry to state the obvious but did you check the address you are using carefully, if using IE it may not cope as well as firefox does with partial addresses
• have you tried http://www.mozilla.com/en-US/firefox/all.html
• if you think McAfee is the problem, then temporarily disable it ( McAfee may block installation attempts but it should not block firefox/mozzila sites for no good reason)
• McAfee will probably block changes/installation of a new browser, unless you either disable it or modify its settings

Check your McAfee configuration against the information in the link on the following page that applies to your McAfee product: http://support.mozilla.com/en-US/kb/Firewalls

OK, I got to the bottom of this issue. Mcafee on install blocked "relevant knowledge". Just took a stab in the dark and removed the block. The 404 not found no longer exists and Firefox is working again. Time to rebuild my bookmarks.

McAfee blocked Relevant Knowledge because it is considered spyware/adware. Did you scan with McAfee to see if it offers to remove Relevant Knowledge? Also see other Malware scanning tools below (all free).

Some old information links about Relevant Knowledge (just read these):

• http://www.ghacks.net/2009/05/18/about-relevant-knowledge/
• http://www.spywareguide.com/product_show.php?id=488
• http://www.ehow.com/how_5634500_remove-relevant-knowledge-spyware.html
• http://www.spywareremove.com/removeRelevantKnowledge.html

Some newer links about Relevant Knowledge (just read these):

• http://forum.avast.com/index.php?topic=63129.0
• http://www.computing.net/answers/security/relevant-knowledge/28740.html
• http://www.spywareremove.com/removeRelevantKnowledge.html
• http://answers.yahoo.com/question/index?qid=20100623212924AAmTa0s

Malware Removal
Download, install and update as many of the following as possible until your infections are cleaned.

1. The free versions of these scanners will detect infections and clean your system; no need to purchase
2. Different malware scanners detect some malware that other scanners do not.
3. If you are unable to download the malware programs,
   • change the name of the installer program before saving the download to your hard drive, and
   • once installed, go to the installation folder for the program and change the name of the program executable file (i.e., for Malwarebytes Anti-Malware, change mbam.exe to xyz-mb.exe), then update the program and run the scan.
   • you may need to download on an un-infected computer, change the name of the installer program, copy the installer to a CD or USB thumb drive, and transport to your system for installation.
4. Some stubborn malware will need to be removed in Windows Safe Mode with Networking. See:
   • http://www.pbcomp.com.au/using-windows-safe-mode.html
   • http://www.malwarehelp.org/restart-into-safe-mode-how-to-2010.html

• Malwarebytes' Anti-Malware - http://www.malwarebytes.org/mbam.php
• SuperAntispyware - http://www.superantispyware.com/
• AdAware - http://www.lavasoftusa.com/software/adaware/
• Spybot Search & Destroy - http://www.safer-networking.org/en/index.html
• Windows Defender - http://www.microsoft.com/windows/products/winfamily/defender/default.mspx
• Dr. Web Cureit - http://www.freedrweb.com/cureit/

If these don't find or can't clear the infection(s), post in one of these forums for specialized malware removal help:

1. Read and follow their rules for posting
2. Follow their instructions to the letter
3. Be patient; you are put in a queue and you will get a response when they get to your post

• http://bleepingcomputer.com
• http://www.spywareinfoforum.com/
• http://www.spywarewarrior.com/index.php
• http://forum.aumha.org/