I'd been having this problem for awhile too, under various ver-
sions of Firefox.  The other day though, I did something that seems
to have fixed it (not that I'm 100% certain that these actions
caused the improved behavior, but I don't know what else would've).

  First, I went to the

    about:config

page to check out the print settings (i.e., I put "print" in the
Filter: field).  Not being sure exactly what to adjust, I started
by doing a right-click Reset on all the non-default-valued entries.
No, that wasn't much fun...  Then I closed firefox, re-removed the
compreg.dat file and re-started.  Now I can finally print that
mapsonus.com page which I so desperately needed last week (a little
too late, but maybe it'll keep working for whatever comes up next).

  If it matters: some time ago, I imported existing Mozilla set-
tings into an earlier version of Firefox--so maybe I had garbage
in my printer config from that.

Cheers,  --Dave