This blog post has been referenced in a couple of places regarding DNN Browser Compatibility: http://www.dnnsoftware.com/blog/announcing-dotnetnuke-7/announcing-dotnetnuke-7 but it is a couple years old, and doesn't take into account 7.3. 

I've also read, and understand that DNN Browser Compatibility relies heavily on which skin and modules are installed. 

This question I am posing is: which browsers does 7.3 support, out of the box?

Thank you.

I have just re-designed our company's landing page in DNN 7.3 and have cross tested it on the majority of browsers. The only problem we have seem to run into is some of our buttons and links (roughly 5-6%) do not work in IE8. Other than that, you should be fine.