Use Revo Uninstaller Portable in Advanced Mode to remove the 32-bit version and all its related files.

Then proceed to install the 64-bit version.

It is possible that security software (anti-virus, firewall) is causing the problem. Try to disable security software temporarily to see whether that makes a difference.

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen or hold down the Shift key) to see whether that works better.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

af24us said

I just got a new 64 bit WIN 10 laptop and downloaded the latest firefox from mozilla.org (July 2017) and somehow mozilla.org website incorrectly automatically downloaded and installed the 32 bit version 54 even though I have 64 bit WIN 10. After a few days I realizing the performance problems I manually downloaded 64 bit firefox 55. However I tried uninstalling firefox 32 bit ver 54 and It wont uninstall because it keeps falsely detecting that firefox is running and wont uninstall while it thinks its running - Its not running in the foreground and I dont know why it wont uninstall and the new 64 bit install package will not remove the old 32 bit package. Any and all suggestions are appreciated - Alan - af24us@aol.com PS - this is why I hate Windows :-) so many bugs

The Revo Uninstaller worked - Thanks for the tip ! However Revo also exposed the many many registry entries and many many other accesory files - not just profiles, cache, history, etc... left behind by Mozilla Uninstaller - Revo allowed me to delete all those as well. I wish I took screenshots to Show Mozilla developers what the Mozilla Uninstaller missed

I don't honestly know if it's a problem with Firefox or with the way you need to code programs in Windows.

Windows Registry is a total mess and I normally use Revo to get rid of all remnants of a program when I want to remove it.

Never experienced such a thing with Linux or OS X.