This is just a wild guess, but do the links to the pages you were clicking on have very long bits of text? (ie, very wide horizontally)?
Also, do you have a nVidia video card. If so, then this is likely a dupe of bug 46034 https://launchpad.net/distros/ubuntu/+source/nvidia-glx/+bug/46034 -- Dapper: firefox 1.5.0.3 crashes on certain sites https://launchpad.net/bugs/46153 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
