I'm using Bitstream Vera Sans as the sans-serif font in Firefox 11.0 beta for Windows 7 x64. There is a drastic jump in size from 16(pt?) to 17(pt?), to the point where 16 is barely legible, and 17 takes up too much space. I tried changing the value to 16.5 in about:config, but it told me that 16.5 isn't an integer (which it isn't). I fell in love with this font, so is there any option beyond dropping Vera?
Open the images in a new tab for full size. As you may be able to ascertain from the screenshot, I'm a fairly serious Wikipedia editor, and it helps to be able to read a lot of text at once, but I still need legibility.