I've installed Ubuntu 12.04 recently, using Gnome classic not Unity.

I have an issue with Thunderbird (currently version 17) when I scroll through emails or select them to view the application hangs.
I see 'Thunderbird' and 'dbus-deamon' listed in 'processes' using 40-50% of the cpu, thunderbird goes 'dark' and I'm unable to click on anything until it releases about 10-20 seconds later.
I could put up with this for a while, but its really annoying now.
I've disabled all plug-in's thinking it was that.
Any ideas?