When you say "clean install", do you mean that you also manually erased the C:\program files\mozilla firefox folder before installing, to remove any remaining files from a previous install?

If so, it seems there is a problem with your profile. Have a look at https://support.mozilla.com/en-US/kb/Basic%20Troubleshooting, and perhaps more specifically https://support.mozilla.com/en-US/kb/Basic%20Troubleshooting#w_8-make-a-new-profile and follow the instructions there for how to test if the problem goes away with a new profile.

Just post back here if you have questions.

Tried renaming the profile (only one listed) thru appdata menu on users subdirectory. Did not fix the problem. Tried installing 7.06b (beta) with same result.

Tried installing Aurora and it worked without a problem. Guess I will use Aurora for foreseeable future.

Note: Clean install means I uninstalled the previous version before dwonloading and installing the newest version.

This has only happened on my desktop computer. Will see if the same thing happens when I try to upgrade my laptop.