Here is my solution to my own problem. So I have a 26 inch CRT HDTV, pretty unusual, and it upconverts 720p to 1080i like most CRTs, I don't know if that matters but FYI.
My problem was that the default install of YDL gave me super tiny text and super tiny icons. I thought I could change the default resolution to fix that, and tried a few things like 480p fullscreen which actually looked good but the edges didn't fit which was super annoying - anyway what I ended up doing is changing some options. First go into configuration options, which is somewhere near the bottom of the list that comes up when you click on the screen, and select font options, and then you have to manually change the font size from 10.0 to 20.0 or whatever size you prefer. I can't remember what categories I figured were important but they are like menu title, menu list, crap like that. Anyway, if you click apply and then open the menu then you will know it is all good.
To change the size of the icons on the screen go into shelves, then right click or something to get into shelf options, and there are all sorts of options. I thought the default shelf was horrible, but there are actually some cool things you can put on there, but you have to enable some of them first through 'modules.'
When you open Firefox the type will still be tiny but you can increase it by pressing ctrl+ a couple times.