I like to use Google Webfonts on my commerical works, but they render a bit too jagged, though in the preview provided by Google, they render very smooth.
Check this
Fonts render differently based on:
Based on the fact that your fonts look worse in Chrome and Firefox the only thing you can do to try and get those browsers to render them better. Without seeing your code the only things I can recommend are:
Making sure you are using decent reset css (something like this: http://meyerweb.com/eric/tools/css/reset/).
Try adding font-weight: normal;
to fonts to see if this makes a difference; sometimes browsers and frameworks try adding a fake bold to things.
Assuring you are using the actual versions of the fonts and not just applying CSS styles.
If all else fails then try bumping the font-size up/down a small amount and see if the font hints better at these sizes.
Hope this helps!