I've been using the Video DownloadHelper for quite a number of years and have found it to be a really useful extension. The way it works is if you are viewing a video on a website that does not have a facility to download the video to your hard drive, the VDH extension will allow you to do this, it will allow you to specify where you want to save it (which folder) and will allow you to specify a pernonalised name for the video that you are saving.

The only downside I found is that you only get told, after the fact, that you should install a secondary extension to be able to save the video. After the installation, and after your first attempt to download a video, you get a prompt to add a secondary, accompanying extension which allows you to save your files effectively. That's just a minor annoyance which quickly dissipates once you learn how useful this extension can be. It will even allow you to download a Youtube video with options of varying quality.