This is an unfortunate side effect of improved security, see https://www.mozilla.org/en-US/firefox/68.0/releasenotes/#fixed ("Local files can no longer access other files in the same directory.").
As a workaround, try changing the value of the 'privacy.file_unique_origin' preference to 'false' in about:config. Please note that this is unsafe, and should be used only for testing purposes, and reverted to the default value afterwards. ** Changed in: firefox (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1836641 Title: 18.04 firefox - broken for xml display To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1836641/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs