Been pulling my hair out debugging a relative’s persistent BSOD (once every ~6hrs) after nudging them to take the first degoogling step by switching browsers.

I could not believe at first that a user space program, especially a Windows Store sandboxed one, could affect anything in the kernel, but analyzing every single coredump shows the exact same trigger: Firefox attempted to rename the UrlAssocistions/http registry key in the UWP sandbox’s virtualized registry hive, triggering an access violation in the Registry system service and crashing ntoskrnl.

It turns out that there is a secretly enabled config “browser.shell.setDefaultBrowserUserChoice.regRename” that causes Firefox to attempt this renaming periodically despite the user already having unchecked the “check if default on startup” option. A quick search reveals that it was a vestigial A/B testing feature that was already slated for deprecation[0], but remained in the current version and a perfect storm of I’m guessing UWP kernel memory bug and Firefox dark pattern triggered this outcome.

[0] https://bugzilla.mozilla.org/show_bug.cgi?id=2060861