I can confirm that starting firefox with LD_PRELOAD=/usr/lib/libXt.so.6 /usr/lib/firefox/firefox
fixes the problem, although the details of my problem is slightly different from in the original post: * Adobe Reader 7.0 does show up under about:plugins in firefox * The error message above (LoadPlugin: ... XtCalloc) does not show up when firefox launches, but when I try to access a PDF-file, and then shows up twice each time. mozilla-acroread version 7.0.1-0.0.ubuntu1 firefox version 1.5.dfsg+1.5.0.4-0ubuntu6.06 -- acrobat plugin not working https://launchpad.net/bugs/50496 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs