Why is Thunderbird pegging a core at 100%?
Change the configuration key
mail.db.idle_limit
to
30000000
In Preferences->Advanced->General->Config-editor
Source: http://rainbow.chard.org/2013/02/19/thunderbird-high-cpu/
Have you tried hiding the status bar? ( View->Toolbar->Status bar ) For me it seems that the animated progress bar uses vast amounts of CPU.