This is a well known Mac thing, and its one of the top 5 reasons why I moved away from OSX and refuse to support Apple users. Safari enforces the OSX "thick antialiasing", causing really thick fonts. This also causes really thick fonts, unreasonably so, in normal non-web apps. The reverse, unfortunately, is true: a lot of web developers worship at the altar of Apple, and have screwed up perfectly good websites by mak…
Some people are passionate about fonts. I think I am the opposite, I override all custom styles with a single font family and a very limited range of sizes. I can just hear designers crying out, but long ago I started doing to that, the web looks so much better when that design decision is eliminated. Even good use of fonts unnecessary.