Affected versions

• Firefox 77.0

Affected platforms

• Windows 10 x64

Preconditions:

• Make sure there is no Firefox installed or running on the pc.
• Run the following commands in CMD:
  rd /s /q %userprofile%\AppData\Roaming\Mozilla
  rd /s /q %userprofile%\AppData\Local\Mozilla
  rd /s /q %userprofile%\AppData\LocalLow\Mozilla

Steps to reproduce

1. Install the Firefox Stub Installer.
2. Finish the process.

Expected result

• The process is finished successfully.

Actual result

• An error appears on the screen, even though the build is installed.

Regression range

• I can't find the regression for this issue, because the stub installer always installs the last version.

Additional notes

• This happens even if the user tries to update or when an older version is being installed.
• This happens even if there are profiles already created.
• In some situations the error "Firefox Installer stopped working" is displayed too.

This sounds like the issue in bug 1600905 comment 13, though we never did get to the bottom of why it was showing up even if there was no instance running, perhaps a shutdown hang? You can run

Get-Process firefox | Select -Property Path

in PowerShell to try to find any firefox.exe on the system. Also you can run the following attached PowerShell script to find any process with the window classes that we look for.

--

But that particular message (WARN_MANUALLY_CLOSE_APP_LAUNCH) was removed completely in bug 1601806, which landed in 74, so I'd think this could only be coming from an old stub. Where did you get the stub you are testing with? If you are still seeing it, could you attach that stub to this bug?

Another possibility is that memory is getting corrupted, leading to all sorts of mischief, for the "Firefox Installer stopped working" message to appear.

I can't seem to be able to reproduce this issue anymore. Only if I try to install older versions of Firefox.
It might be something intermittent or it was a Windows issue that was rectified with the last update.