Please go to www.getfirefox.com, download Firefox 20, and install it.

Maybe you didn't read my problem. I have done this (4 times). After each install, I close Firefox 20.0.1 and reopen to Firefox 18.0.1.

So you are actually downloading the installer? (from the sounds of your question you are using the About Firefox box to download the update).

I don't understand your point. Help/About allows you to check for updates. It finds an update and provides a link to www.firefox.com. I follow the link, select desktop, and download Firefox%20Setup%2020.0.1(5).exe. I have just done this for the fifth time (the previous 4 times, I tried to install). Are you suggesting that www.getfirefox.com downloads a different installer?

Hmm, your Firefox is doing something odd then, About Firefox should download automatically, not point to firefox.com.

Try a clean reinstall:

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove Firefox program files and then reinstall Firefox. Please follow these steps:

Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from http://www.mozilla.org and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (click Exit from the Firefox or File menu).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
   • Mac: Delete Firefox from the Applications folder.
   • Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

Please report back to see if this helped you!

I haven't tried this yet, but it has to work, right? If I wipe 18.0.1 and install fresh, it has to get 20.0.1. It will be annoying, though, if this happens when the next update comes around. I will report back when I try this, but first I'm going to go save my bookmarks!

As for the About behavior, I think the first time I update in each new version I see the behavior you describe, but then it fails and after that just shows the link. I always assumed there is something about my company's firewall that doesn't allow the install the other way, but that's a guess.

Anyway, thanks for your help, and I will come back and respond when I "update."

Which security software (firewall, anti-virus) do you have?

Try to boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if that helps to install Firefox properly.

Sorry this took a while to get back to you. I had to request admin rights to my computer to delete the old Firefox, then the new version installed flawlessly. Nice try, but I don't think I'm advertising my company's security measures.  :)

Thanks again for your help.