This bug has also been reported in Debian:

http://bugs.debian.org/632310

Interestingly there are some difference to what I read here and in the bugzilla report: Accordung to the
bug submitter xulrunner 1.9.1 is affected, too.

Probably a followup error, but possibly also another issue: "Searching the buffer (while otherwise
working, finding results, and highlighting them) does not scroll the buffer to the position of the
current match" don't work in the first buffer either.