Ah thanks god, I thought I’m the only one!
Exactly the same happened to me.
The update from yesterday updated the openjava which multibit uses.
Since then torbrowser crashes all the time when multibit is running
if multibit is closed, torbrowser runs just fine!
I spend the last hour looking for something about it online but I guess very few people use multibit and torbrowser at the sime time inside a VM 
not sure how openjava crashes torbrowser but it’s huge pain in the ass, need a fix urgently
edit:
I also have 4GB or ram so that shouldn’t be the issue
but we seem to have exactly the same setup i_need_support_pls, are you me? 
edit2:
multibit ram use grows to 450mb, firefox to 90mb
still the total in use is 700mb out of 4gb, so plenty of ram to spare
however it goes to a point that torbrowser closes as soon as it’s opened after multibit has been on for a while.
i relate it 99% to the openjava update from yesterday, i had zero problems before that and totally unusuable from today
is there a way to revert it or?