As other reviewers have noted, the new Quantum version has serious problems, so I rolled back to FF 56. But they've redesigned the version for FF 56 as well, and the new redesign is not good. The media list used to be nice and compact, but now the text is bigger and there's a lot of extra white space so you can't see as many files at the same time to choose from. Bad decision!

And there's also a bug. If you try to configure VideoDownloadHelper, suddenly your list vanishes and the extension will no longer work until you restart Firefox.