If it happens on all sites on all browsers, it's an issue with the font(s) on your Mac. It's not clear from this one example if it happens all fonts (like Times New Roman, Arial, Verdana - sorry that are Windows fonts, but you get the picture, I hope) or just with one.
You can experiment by making a simple html-page with different fonts on your own Mac.
Kees
After turning on my iMac this morning, I noticed that all bold fonts in my browser (Safari) were compressed http://tinypic.com/r/2gspymt/6 - I have tried Chrome and Firefox, but the problem is still there
Any ideas or solutions would be much appreciated

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