Comment 6 for bug 1887509

This is really important issue, especially now with surge on new users rushing to Linux. Consider scenario, when new user tries to install Steam: after clicking "Download Steam" button on website Firefox defaults to "Open with Software Install" and pressing OK leaves user stumped with cryptic error message "Failed to install file: not supported". Some users might give up right here, as OS states that package is supposedly "not supported".
If fixing this issue is impossible or too complicated, at least add a helpful error message, that informs user to download package to disk and run it from there.