[Mozilla Enterprise] Can´t open links in Outlook - caused by stale FirefoxESR registry keys, fix?

[André Sänger]

Hello,

some of our Users (Windows 10) reported errors when trying to open links 
in Outlook messages (“Your organization’s policies are preventing us 
from completing this action for you. For more info, please contact your 
help desk”.). I have tracked down the problem to incorrect FirefoxESR 
Registry keys.

In these cases I noticed [HKEY_CLASSES_ROOT\.html] still points to 
@="FirefoxHTML", which in turn contains no 
HKR\FirefoxHTML\shell\open\command.

HKR\FirefoxHTML-E7CF176E110C11B does exist as well and contains correct 
shell\open\command entries but doesn´t get used since HKR\.html still 
points to HKR\FirefoxHTML.

Already tried reinstalling firefox, changing the standard app selection 
via Windows 10 system settings, executing 
[Firefoxpath]\uninstall\helper.exe" /SetAsDefaultAppGlobal command, all 
without success.

As a quick workaround copying the shell\open\command from the 
FirefoxHTML-E7CF176E110C11B entry to the FirefoxHTML one does work, but 
that´s not a proper fix.

Is there a tool/script, that can clean up the old stale FirefoxHTML / 
FirefoxURL entries automatically? It´s not just 
[HKEY_CLASSES_ROOT\.html], there are lots of entries all over the place 
still pointing to the old nomenclature.


-- 
Regards,
André