Hi killtoy, please ignore the spam message with a phone number -- that's not official and we don't know what they will do to your system if you engage.

Hello,

You may have seen a post or received a notification regarding support for Firefox or Thunderbird with a link to another site or a phone number being posted. This is a scam and is not a method to receive support from Mozilla. Mozilla does not have telephone or email support. Please do not click on the link and do not interact by calling any phone numbers or email addresses listed. I apologize for any inconvenience caused. You are currently posting on the official Mozilla website and will receive assistance here.

Hi killtoy, coincidentally (??) a user who appears to have a non-English language Windows reported that error this morning. On that computer,

C:\Program Files

was spelled differently. Do you have that same situation or does that exact path in the error message exist on your computer?

C:\Program Files\Mozilla Firefox\

Other thread (unsolved): https://support.mozilla.org/questions/1290476

There are now 3 of these reported problems.

See if this works ( notice the quotes front and back ) : "C:\Program Files\Mozilla Firefox\firefox.exe"

Another user reported that moving the contents of:

C:\Program Files\Mozilla Firefox

to

C:\Program Files (x86)\Mozilla Firefox

allowed Firefox to run. I don't know why that would make a difference.

https://support.mozilla.org/questions/1290528

Hello!

Thank you jscher2000, moving the program folder from Program Files to Program Files (x86) did indeed work!

Hi killtoy, it makes me a bit suspicious if programs can't run from the normal 64-bit programs folder. What is going on there?

Could this be a problem with the Windows Registry in the key where these default Shell Folders locations are stored ?

• HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders

Here is another key you can check:

• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options => Debugger

More:

• https://www.google.com/search?q=avast+%22Windows+cannot+find%22&newwindow=1&source=lnt&tbs=qdr:w&sa=X&biw=1056&bih=685

Hi!

1st: jscher2000: Honestly, I have no idea. Haven't made any changes to my computer at all, it just stopped working. And I honestly don't know why moving the folder fixed it.

And on that note, the same error popped up on my sister's computer this morning too, and the same fix worked, so thank you for that.

2nd: cor-el: Thank you for that. I do have Avast, and Avast Cleanup, both of which I use frequently. If I run into the error again, I'll let you know if that fixes it.

Would be really annoying if it's Avast breaking file links and registry. -_-

Me again!

So, been struggling with the same error while trying to open Microsoft Word and all related files. I did the fix you suggested, Cor-el, and it worked. Turns out the problem is Avast Cleanup rewriting the value in a program's debugging registry. Simply deleting the Avast value fixes the issue.

Thank you guys so much for the help and your speedy replies, I would never have found the root of the issue or its fix without you. :)

Well done. You should contact Avast support and let them know.

There seem to be a lot of reports on https://forum.avast.com/index.php?board=63.0 so we're just waiting for Avast to issue a fix.

Avast has issued an update for Avast Cleanup that should fix this: https://forum.avast.com/index.php?topic=234798.0