What are the differences between browsers, programmatically?

Solution 1:

Have a look at this article for some detailed, useful information such as:

• Image format support
• Plugins and syndicated content support
• JavaScript support
• Operating system support
• Vulnerabilities

All of this information appears to be kept very current about modern browsers. The article lists some useful information about historical browsers as well.

I imagine that a web developer could find no more informative a comparison without giving up some degree of the breadth afforded by that article.

Solution 2:

http://quirksmode.org/ has some VERY long tables on CSS, DOM and JS support.

Solution 3:

Google's Browser Security Handbook has a comprehensive comparison of popular browsers from a security & development perspective