Press F12 on the keyboard and in the top corner of the panel that pops open is a tool that lets you select and inspect elements. Click on the video to inspect it and a direct link will show up and be highlighted in the new panel. From there you should be able to open the video into a new window and save it from there.
There's also browser add ons you can get for chrome and firefox that add download buttons below the posts, but you'll have to install them manually because chrome removed them from their extension store.
If it's a model that uses the DRM it's a bit trickier.