You can't. :<

Actually, you can make a lot of browsers have larger or smaller text and pictures. In Firefox, it's Ctrl and the Plus or Minus keys to make it larger or smaller. That might do it, but it'll make the text potentially harder to read, and you'll have to resize back and forth a bit with other sites, I would think.

Oh, and to reset to normal, it's Ctrl and the zero key

Greasemonkey + this

Search for "var size" and set the value to however large/small you want your thumbnails.

Gahhhh

Why couldn't he have given us the option like when he changed the background colour?

I'm sure they could have. In fact, they were apparently going to put the option in, but it's like when someone with horrible timekeeping says they'll be "just a minute"... Pull out a book and get comfy :P