Affected versions

• Firefox 100.0b4
• Firefox 101.0a1

Affected platforms

• Windows 11

Steps to reproduce

1. Install an older Firefox version (ex. 99.0b4)
2. Update the browser to the latest version
3. Access about:preferences and set Firefox as default and have opened the Default apps in Windows 11

Expected result

• Firefox is made as default automatically to the supported file types without any other user interaction other than selecting "Make Firefox Default" in about:preferences.

Actual result

• After an update to the latest version, Firefox will duplicate in Default Apps in system and this will force the user to manually select the file types when selecting "Make Firefox Default" in about:preferences.

Regression range

• Can't search for a regression as Firefox will be updating to the latest version.

Additional notes

• The issue can be seen in the following attachment. First the browser is made automatically default without problems if it was cleanly installed, but after updating it, it will simply duplicate and break the default functionality.
• This is affecting Windows 11. Windows 10 and below doesn't behave as Windows 11's default app selections.
• By following the steps, Firefox will not be recognized as an option to select for example PDF handle in Default App in Win 11 settings.
• If Firefox is cleanly installed to the latest build, it will show only once in Default Apps in Windows and will be automatically set by default to the supported file types

Excellent find, Catalin. I hypothesize that I need to remove any existing association for .pdf and FirefoxHTML so there's only the new FirefoxPDF. This migration is probably technically very close to what needs to be done to address Bug 1764290, but it's higher priority since it seems to significantly impact the Windows 11 UX.

Catalin: I can't duplicate this in a fresh Win11 VM :( I'd think I'm going to work on the other 2 tickets, which are at least clearly broken, and then we can revisit this after you get a build with Bug 1763824.

Tested again on 100.0b8 and it seems that after updating Firefox, changing the pref to true and making Firefox as default will behave as expected now (default pdf handler, new icon and file type). Will set this as WFM in this case. Thank you Nick!