Firefox and chrome chewing CPU since updates

[Paul Smith]

So, I was away all week on vacation (during that time my system was
halted and unplugged) and when I got back I had 56 or so updates waiting
for me (Ubuntu 12.04 64bit) including a kernel update and various other
things.

I applied these and rebooted.  Now whenever I start a browser, either
the default Firefox or Chrome (I use the main/stable version from the
dl.google.com repository), it sucks up TONS of CPU.

Firefox is usually chewing at least 60% CPU and sometimes jumps to 120%
or more (I have an Intel Core2 Quad).  top(1) says my system load is
constantly at 1.3 or above.  This is with no extra tabs open and
about:blank on the single tab I do have.

Chrome is even worse, since it's multi-processing: when I start it there
are 3 to 4 chrome processes running each taking between 25% and 45% of a
CPU, and my system load goes up to 2.2 or higher, constantly.

The browsers seem to WORK just fine; I can surf the web and no problems
with internet connections, etc.  Just my system is running like crazy,
not doing anything.

This was never a problem before these updates.  Has anyone else seen
this, or have any idea what's going on?  It's very odd that it's both
Firefox and Chrome, I admit, but if I stop them the load goes down and
none of my other apps (which, admittedly, I don't use too many different
apps--mostly Emacs, rxvt, Evolution, etc.) seem to show this problem.

Has anyone else seen this behavior?  I've tried strace on these but see
nothing interesting: chrome seems to be hanging on a futex (but not fast
enough for the kind of load I'm seeing) and Firefox seems to be failing
to read from a socket (but again, not fast enough for the load).

This is extremely frustrating.