i had an out of memory just a couple of days ago also, and my firefox has been playing up since the updates,
when i ran out of memory i was in the middle of a very fast download, it was storming in at 5+meg.
the reason for the issue was the read and write speeds were too much for bittorrent,
but i still have high ram and cpu readings more than usual, im sure,
its not something i kept much notice of until this week.
im not sure the updates are related to my firefox issue but the more people mention it then there may be a connection.
sorry i cant be of assistance but adding to see if it is a recent pattern for people.