I’ve searched around a little for someone to mention this problem, but I haven’t found anything beyond some Ubuntu solutions. I’m using SUSE 11.1 and just updated the latest Firefox (3.5.3). Now it seems some of my fonts in the browser are all bold. I think perhaps just the ones the browser chooses as a default.
I have a similar problem. Some fonts in Firefox 3.5.4 and 3.0.14 are bold while others are just fine. I have been searching the web and have not found any solution yet. If I find a solution I’ll share it here.