It's possible that the issue lies with the browsers and not the Mac if the problem is isolated to web browsing. Does this only happen with web pages? Does it happen with every page?
EDIT: Just took a look at that page in Opera on Windows and it looks very similar. The difference I see may be because of my eye sight or the fact that I'm using a different browser on a different platform. The difference could also be because of the quality of your image.
Shop for your Apple, Mac, iPhone and other computer products on Amazon.
We are a participant in the Amazon Services LLC Associates Program, an affiliate program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.