The Tomboy error message might be caused by any number of things; the only buttons that work on *my* web browser are home and reload, until I visit another webpage, so that's perhaps not unusual (but, of course, is if you have been browsing other pages - I don't mean to be flippant). Far more worrying is the failure of Opera and Thunderbird to run. I suspect that your gtk 2 installation is corrupted, but am not sure.
It would help people to solve your problem if we had more information - try running Opera or Thunderbird in a terminal and posting any error messages here. Also, running
will check for any broken dependencies you might have.