User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:83.0) Gecko/20100101 Firefox/83.0

Steps to reproduce:

Environment: Windows 7 running on a PC.
OS default mail client: Microsoft Outlook 2007

Clicked on envelope (mailto) icon to send page link by email

Actual results:

Firefox opened a flood of tabs threatening to crash the machine. The speed of opening prevented the use of Task Manager to kill the process. Needed hard shut down. On restart the default Outlook mail account was corrupted and required repair.

More info in my recent posts in connection with Bug 510009.

Totally new to bug reporting - although a long standing Firefox user - so apologies if the way in which I'm going about the report breaches any protocols.

Expected results:

Clicking on the mailto icon should (and had previously) resulted in Outlook opening with a mail message interface.

Hi Jack, see bug 215554?

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

(In reply to Release mgmt bot [:sylvestre / :calixte / :marco for bugbug] from comment #2)

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

(In reply to Andre Klapper from comment #1)

Hi Jack, see bug 215554?

Yes, Andre. Thanks for the pointer. There seem to have been various iterations of this bug going back 18+ years. In my case, it appeared after the change to Firefox 83.

I think that answer - from the 215554 thread - is here:

Problem: Mozilla goes into an infinite loop of opening new browser windows and

creating new copies of a file that is trying to be opened. This occurs when
Mozilla is set to automatically open the file with the default application and
Windows has Mozilla associated as the default application for that filetype.

When I discovered that Firefox had changed the mail handler ("mailto") association in Windows "Default programs" to Firefox, I also noticed that the .pdf extension had become associated with Firefox (rather than Adobe Acrobat as previously set). So, I suppose it is a bug in the sense that something working previous doesn't work as a result of an update.

The severity field is not set for this bug.
:Gijs, could you have a look please?

For more information, please visit auto_nag documentation.

Oops, looks like Jack and I both filed a separate bug here - we only need 1 to track this, so I'm going to mark this as a duplicate.