I recently discovered this firefox\chrome extension that make streaming videos soo much faster. It also has built in subtitle support that lets you upload subtitles or search through opensubtitles. It’s incredible how much faster videos load https://github.com/Andrews54757/FastStream
Looks like it mostly just buffers the video more aggressively. If you have a good Internet connection it won’t do anything useful other than peg the server’s connection downloading the entire video file at gigabit speeds and make it worse for other viewers.