Below is my previous question which led me to the first work around. https://support.mozilla.org/en-US/questions/1173413

Others have reported problems with 64-bite while 32 has no problem.

I just posted on the old thread here https://support.mozilla.org/en-US/questions/1173413, before I found this thread, but in summary I can confirm that I too am having this problem on one PC. I'm convinced that this is something in the registry, but cannot locate the issue... Very frustrating :(

PS: Windows 10 Pro

Allan2, the only way I managed to keep using firefox is installing an older 32bit as described and let it update to latest 32bit version. 64bit is a complete no-go for me and since I cannot seem to get an answer on how to actually fix the issue, 32bit will be until a fresh windows installation or until i get fed up and move to another browser.

Good luck!

PS. well, now that recent update to 56.0.1 is to migrate 32bit user to 64bit, I am guessing my home computer will not be able to run firefox anymore. Will update this thread when I have updated but I suspect its time to look for another browser.

As expected, upon update and migration to 64bit version, firefox is again not starting. Unless I can get a real answer to this I am quitting Firefox.

Hi rpaulino, I suspect that something in the upgrade process caused some key in the registry to be corrupted - one that is not removed by the uninstall software or Ccleaner once FF is uninstalled.

I suspect that only a complete refresh of Win 10 might resolve the issue, but that is a drastic approach with the need to reinstall applications. If that failed, then a reinstall from the ISO for Win 10 would almost certainly work.

Perhaps, if we're lucky, the new Win 10 update might clean it out - but I suspect not.

I'm afraid that for now, I've given up on FF for that computer and gone back to using Edge (which is not as bad as some make out). Pity really as I do prefer FF.

Surely one of the developers at Mozilla could suggest some registry keys to check. Anyone?

First, I am sorry to hear that the only work around in this thread are renaming the firefox.exe file or downgrading, this is not an ideal situation. You need to also make sure you have 64-bit version of Windows 7 or higher. Firefox 64bit will not run on 32bit version of windows. So if we are going to use an ISO, please make sure it is the 64bit version of Windows.

I don't think we have to go as far as an ISO re-install, unless that is the case that you have Windows 7 32bit.

After you have updated to the Windows 64bit version, please start Firefox with the profile mananger to manage your profiles.

1. Open cmd.exe
2. Paste "C:\Program Files (x86)\Mozilla Firefox\firefox.exe" -P
3. Then hit enter
4. Does Firefox start? Choose the profile, that includes 'defualt' if you recieve an error, create a new one.

Then follow the instructions on how to move over the profile info into a new profile - Profile Manager - Create, remove or switch Firefox profiles

If Firefox does not start, please let me know. We can also get a new stub installer - with these instructions

Thanks guigs for taking the time to respond. I had tried all of the fault finding techniques including the one you outlined above. Firefox will not run even with the -P option.

Besides, I completely removed it, including all directories related to Firefox both in Program directories and Data directories and then reinstalled it from scratch. Even that did not work.

Even an install of an earlier version did not work.

To be clear this is on a 64Bit Windows 10 PC. I gave up on that PC.

In that case I would use CCleaner to clean up any corrupt registries and start from a new official install. How to install Firefox on Windows

Thanks but I tried that and yes CCleaner removed quite a few Mozilla entries. Interestingly the registry still has a few when I do a manual search in Regedit, but MS also seem to put certain entries there for Mozilla and Symantec and a whole heap of products even on a fresh Windows install so I don't dare touch those.

This one is a truly weird problem. I'm certain that something failed on the update and resulted in a corrupt registry entry somewhere, but given CCleaner does not remove it, I'm not sure how I could find it.

I've been using Chrome (wash my mouth out for saying that :) )

This can also happen if you have software that hooks into Firefox that isn't compatible with 64-bit Firefox. You can check the Windows Event log to see if there are details about these failures.

Yeah its now been several weeks since I was trying to work through all this, but I did check the event logs at the time. I remember there was an error with the Faulting Application path being c:\....\ Firefox.exe and the faulting module of ntdll.dll.

A Scannow and DISM report did not show any Windows problems, so...

I don't think the problem is Firefox per se. But neither does it appear to be a Windows problem. It is weird that all was fine until the update of Firefox, but...

I really think the only way out of this will be a complete rebuild of Win 10 on this machine and a fresh install. Until I have time to do that (probably in January), I don't think I'm going to get anywhere with this one and have given up.

I appreciate people's efforts.