Same for me, everything ran great until I upgrade to Raring from 12.x
Firefox 20.0, Thunderbird 17.0.5
The only thing I recall about upgrading is that new nVidia drivers were install during the upgrade.
I was not using Oxygen GTK theme, I was using the Air Black Remix for Window Decorations and Glassified for desktop theme.
Switched both anyway to see if that helps.
Same for me, everything ran great until I upgrade to Raring from 12.x
Firefox 20.0, Thunderbird 17.0.5
The only thing I recall about upgrading is that new nVidia drivers were install during the upgrade.
I was not using Oxygen GTK theme, I was using the Air Black Remix for Window Decorations and Glassified for desktop theme.
Switched both anyway to see if that helps.