Ok, "any file" was wrong. The problem appears to be "any file in the /tmp hierarchy". That is a common destination for downloading and unpacking stuff, including by software that displays HTML by reverting to the system browser.
The error message then is File not found Firefox can’t find the file at /tmp/test-results/index.html. Check the file name for capitalization or other typing errors. Check to see if the file was moved, renamed or deleted. -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to firefox in Ubuntu. https://bugs.launchpad.net/bugs/1977782 Title: Unable to open any file:/// URL Status in firefox package in Ubuntu: Incomplete Bug description: The way this configures/installs the snap makes it impossible to open any file either from the command-line or by specifying a link of the file:/// kind. That makes firefox unusable for browsing local HTML documentation. ProblemType: Bug DistroRelease: Ubuntu 22.04 Package: firefox 1:1snap1-0ubuntu2 ProcVersionSignature: Ubuntu 5.15.0-35.36-lowlatency 5.15.35 Uname: Linux 5.15.0-35-lowlatency x86_64 ApportVersion: 2.20.11-0ubuntu82.1 Architecture: amd64 CasperMD5CheckResult: unknown CurrentDesktop: XFCE Date: Tue Jun 7 02:27:27 2022 InstallationDate: Installed on 2011-10-14 (3888 days ago) InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111011) Snap.Changes: no changes found SourcePackage: firefox UpgradeStatus: Upgraded to jammy on 2022-01-28 (130 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1977782/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp