It's a great addon indeed
Sorry i only just saw this...
I actually normal have this installed to remove all the crap, instant 720p, bigger video and pause the video until im ready to watch it, i admit i like this extension just have not got around to installing it im also in two mids on re-installing everything computer is feeling sluggish so might wait for abit but yes it is a good extension!
As for downloading, my download folder has enough rubbish lol i dont want to download something im probably only going to watch once.
Might be worth testing with it to see if it improves the situation prior to trying my download idea
Also, you could try turning on the HTML beta in YouTube, that might help out