There is an extension that is intended to export HTTP tracing data
(include timings) from the Net panel.
See more info here:
http://getfirebug.com/releases/extensions
The export is currently done manually by clicking a button, but
perhaps some kind of an auto export feature could be a nice addition
to it.
Please report a new enhancement bug with a description how it should
work here:
http://code.google.com/p/fbug/issues/list
Honza