Nathan Mische's AMF Explorer is a nice add-on for Firefox which allows to seamlessly debug AMF traffic from within Firefox. Looks very promising, especially as the capturing of the AMF packets seems to be written in JS (not sure, though).

https://addons.mozilla.org/en-US/firefox/addon/78928

Update: Nathan confirmed that the add-on uses an JS to deserialize the data. The implementation is based on the BlazeDS java code. Nice job!

Dirk.