File dialog sometimes fails to open

Greetings,

Workaround for a problem with containerized Mullvad failing to launch a file dialog.

Expected behavior works on the related Tor browser:

1. Ctrl-O opens a file dialog to choose a local file
2. File -> Save Page As can open a file dialog
3. Bookmark Organizer -> Restore -> From file can open a file dialog

On Mullvad:

1. works as above
2. silently ignored
3. silently ignored

What appears when run with --log:

Mullvad Browser:14): Gtk-CRITICAL **: 20:34:43.030: Unable to create user data directory '/home/mullvad/.var/mullvad-browser/Browser/.local/share' for storing the recently used files list: Not a directory

Both Tor and Mullvad beget Browser/.local/share symlinked to /dev/null. Replacing this with a directory is the workaround.

My environment may matter:

Those browsers are both in the same Arch Linux container, with a variant of Ubuntu as host.

||/ Name              Version                                         Architecture Description
+++-=================-===============================================-============-=================================
ii  systemd-container 249.11-0ubuntu3.11pop0~1704473387~22.04~3ce38bf amd64        systemd container/nspawn tools

systemd-nspawn was chosen because only a few extra options are needed to permit browsers to play audio.

On Arch, the dependencies for Firefox are installed and the choices during that installation were noto-fonts and pipewire-jack. Tor Browser is installed from the Arch Linux torbrowser-launcher package. Mullvad browser is simply dropped into place from the 13.5 tarball.

Outside of this containerization, Mullvad on the host machine runs fine with Browser/.local/share symlinked to /dev/null.

Issue: https://github.com/mullvad/mullvad-browser/issues/267