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The directory chooser won't allow showing of, or navigating to, hidden folders on Linux (those with a dot as the first character in their name). This makes selecting a Firefox profile with the directory chooser impossible in Tools -> Options -> Miscellaneous -> JavaScript -> Firefox Profile Location, as Firefox profiles are in a hidden folder (.mozilla) in a user's home directory (e.g. /home/someuser/.mozilla/firefox/8888888.default/). (The profile location can be typed in manually, so this is mainly for convenience).