I've been using Get them all downloader
for at least 5 years and recommend it to anyone who is still looking for a way to download porn from free sites like pornhub or pron.tv.
Why do I download free porn? Cause I like to have a backlog and when I'm bored, I go through my old drive one by one with stuff I'm already into.
It works on 90% of all main tube sites but has about a 30% reliability on sites like sexix.com or any site that uses a jwplayer player for their site but it honestly matters jack all cause you'll probably find the same video from the other tube sites. In uncommon cases, if the player they use is weird, namely xvideos.com and xxnx, you can still download it but the extension appears to be forced to convert the video into a format it likes i.e. .flv instead of downloading it directly as a .m4a by which the process is not very "smooth". You can download videos fine but you'll see once you start skipping the video for different scenes.
For those sites, I'd recommend just registering at xvideos (free) so you can use the supported downloader on the player to download it natively as a .m4a and have zero issues with playback.
Noted supported downloads: openload, google drive, tumblr videos.
To download videos, just change the tab to videos and it'll show all the video content on the page you can download. If it's not there, try playing the video so that the extension can recognise it.
I liked this extension in particular cause it's not ugly as shit and doesn't leave ugly buttons crammed next to every video you see.