To install, drag the link below into your bookmarks bar. Then, navigate to a page of sourcecode, and click on the bookmark named "Highlight Syntax"
Here's a JavaScript source file you can test it on. Or, you can try it on a C file.
The link above is a bookmarklet, a small JavaScript program that can be run on any webpage.
It's based on SHJS and should support any syntax SHJS supports.