Execute python code inside browser without Jython
nosklo's answer is wrong: pyxpcomext for firefox adds language="python" support to script tags. yes it's a whopping 10mb plugin, but that's life. i think it's best if you refer to http://wiki.python.org/moin/WebBrowserProgramming because that is where all known documented links between python and web browser technology are recorded: you can take your pick, there.
I put together a table comparing many Python-In-Browser technologies not long ago:http://stromberg.dnsalias.org/~strombrg/pybrowser/python-browser.html