Your page looks fine on my browser (Chrome under Windows).
Different browsers all render text differently. What you will find is that there are often sweet spots in font sizes that look better than others. In any case, what you are talking about is whether the browser is displaying fonts anti-aliased or not.
There is a CSS3 property, font-smooth
, that you can adjust for this, but don't expect it to work on browsers that aren't smoothing their fonts anyway. You can read about it here: http://webdesign.about.com/od/styleproperties/p/blspfontsmooth.htm
In short, don't worry about it. If it is a big deal for you, then experiment with different fonts and sizes. A good tool for doing this is at http://www.typetester.org/
Don't forget to test your site at BrowserShots.org. It will do screen captures for you, so you can check these details on a wide range of platforms.
If you must have your font rendered in a specific way, then it must be done in an image. This is not recommended. Text should be text wherever possible. However, if you must do it this way, consider one of the many scripts that assist, so you can keep text for browsers that don't support the script, and SEO isn't a problem. Typeface.js is commonly used for this.