Firefox changed fonts this morning (post-update?)

[Jason]

Binary package hint: firefox-3.0

Using Intrepid (9.04), firefox 3.0.11, system updated 29 Jun 2009.
My system did some upgrades this morning (I don't know whether firefox was updated, or a different package) and now Firefox is using different fonts - for the menus etc not just the web sites being browsed (not such nice ones either - the main font is "thinner").
I will gladly provide additional info if somebody can tell me what to supply (or what to type to get it!)
Other gnome etc apps are fine and my guess is that it has reverted to some kind on non ubuntu customized version as the fonts are "sane" but not what I would expect.

firefox:
  Installed: 3.0.11+build2+nobinonly-0ubuntu0.9.04.1
  Candidate: 3.0.11+build2+nobinonly-0ubuntu0.9.04.1
  Version table:
 *** 3.0.11+build2+nobinonly-0ubuntu0.9.04.1 0
        500 http://gb.archive.ubuntu.com jaunty-updates/main Packages
        500 http://security.ubuntu.com jaunty-security/main Packages
        100 /var/lib/dpkg/status
     3.0.8+nobinonly-0ubuntu3 0
        500 http://gb.archive.ubuntu.com jaunty/main Packages

ProblemType: Bug
Architecture: i386
DistroRelease: Ubuntu 9.04
NonfreeKernelModules: nvidia
Package: firefox-3.0 3.0.11+build2+nobinonly-0ubuntu0.9.04.1
ProcEnviron:
 PATH=(custom, user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: firefox-3.0
Uname: Linux 2.6.28-13-generic i686