Review Mozilla 1714583: UNC shared folder as default download location not working on Windows 10 (because nsIFile::exists() returns false for network server names on Windows)
https://bugzilla.mozilla.org/show_bug.cgi?id=1714583
This patch fixes an issue whereby users were unable to save files to a UNC shared folder. We have a few other issues in the past with UNC paths (some unavaoidable iirc) for refernence:
We should figure out what the right behaviour is here, maybe revert the above Mozilla fix or more actively prevent UNC path access.