Junkbuster 2.0 definitely does not support HTTP1.1, and there are some comments in the Mozilla bug databae that indicate it plays fast and loose with HTTP requests under any circumstance. It appears Junkbuster has halted development of the proxy, with its website actually recommending a commercial product these days.
A group at [link|http://sourceforge.net/projects/ijbswa/|Sourceforge] has taken up the slack and is working on the 3.0 version. I've been running the 2.9 alpha version since Mozilla 0.9.7 and I haven't had a single horked URL since.