Been using this add-on for years. It is by far the best video download add-on I have ever come across (nothing for Safari, Chrome or Edge comes close) due to the sheer number of web sites it will work on.

Video Download Helper can download videos from just about any web page containing an embedded video. If it can't download a video directly, it will use another method (after the user installs one or two helper utilities - a little inconvenient, and for some users a little confusing, but well worth the trouble).

This Firefox add-on gets my highest recommendation.