This is needed for Ubuntu Linux when Firefox is installed as a Snap package.
Under those conditions, Firefox doesn't have the ability to read the contents
of the other browsers' data directories.
We work around by showing the user a native file picker and instructing them
to browse to that data directory in folder picker mode - doing so gives
the Firefox process access to the folder (through a temporary symlink).
Another restriction we must overcome is Sqlite's inability to read from
Sqlite databases through that symlinked folder. We work around this by
copying the databases we're importing from to the system temporary
directory, querying it, and then deleting those copies.
Differential Revision: https://phabricator.services.mozilla.com/D188874
e1336c1a0f