further to earlier grumbling about firefox, it seems the main culprit is the restore-session facility. This is something I hated anyway, even without realising that it was shutting down my hdd every 10 seconds to churn through all my tabs. Solution: go to about:config. browser.sessionstore.interval controls how often firefox stores its tab data. The default is 10 seconds; setting it to a long string of nines has sped up my computer no end.
and so, firefox is saved for another day.
also of note: the vimkeys plugin, providing j/k scrolling.