It is possible that security software (anti-virus, firewall) is causing the problem. Try to disable security software temporarily to see if 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 if that has effect.

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

smith.kian said

"EXECUTE PATCH firefox.exe rename_file: failed to rename file - src: C:\Program Files\Mozilla Firefox/firefox.exe, dst:C:\Program Files\Mozilla Firefox/firefox.exe.moz-backup, err: 13 ### execution failed"

That is weird: Windows paths should never have / between the folder name and file name. Is that a glitch in the updater or in the error message? Hmm...

Considering the program folder name: Is the problem with the Windows 64-bit release on 64-bit systems, or the Windows 32-bit release on 32-bit systems?

The problem is happening with the 64-bit Windows release on a 64-bit system.

I assume that the logging code is using Unix convention for appending the file name and prepends the directory path that is of course containing backslashes on Windows.

• https://dxr.mozilla.org/mozilla-release/source/toolkit/mozapps/update/updater/updater.cpp

It would take a lot of code to check what platform is used.

The only reasons for issues with updating that I can think of would be the (write) permissions for the file and other software keeping a possible handle on the file that prevents Firefox from deleting or renaming files.