The Inspector currently doesn't really have an AJAX or XMLHttpRequest support. Firebug shows lots of information about when XHRs were sent/received and what information they contain. This is the umbrella bug representing making our AJAX support at least as good as Firebug's.
Committed revision 31922.
Reopening since we still have some unresolved blocking bugs (bug 14313 and bug 17233 at the moment). I also remove bug 6590 as a dependency, since it doesn't really have anything to do with XHR.
Added a couple other bugs 20322, 20323
Added 22920 which is related