For some strange reason, Acrobat 9 + seems to crash seconds after opening a PDF document in Ubuntu Jaunty. Doubtless other Linux users may experience this in their different distros. It happens both as a standalone PDF and in the Firefox plug in. There does not seem to be a workaround or fix for the moment. My solution was to uninstall Acrobat reader 9 and install Acrobat Reader 8. That works fine. I'll put AR9 back on when Adobe sorts out the problem