12.04 slows down when watching videos

[Jim Byrnes]

Running Ubuntu 12.04, Firefox 36.0.1 and Chromium 37.02.2062.120 all up 
to date.

Over the last couple of weeks when I watch youtube videos my machine 
gradually slows down and become unusable.  The mouse gets jumpy and if I 
try to open or close a window it does it in stages  and take 5 or 10 
seconds to fade in or out.  I've tried Firefox and Chromium with the 
same results.  Today I was watching a video on NHL.com with Chromium and 
the same thing happened. If I don't watch any videos the machine will 
run without any slow downs for as long as I care to run it.

I took a snapshot of top when this was happening maybe it shows something.

jfb at jims1204:~$ top

top - 14:49:02 up  5:46,  2 users,  load average: 0.97, 1.60, 1.09
Tasks: 202 total,   2 running, 200 sleeping,   0 stopped,   0 zombie
Cpu(s):  6.6%us, 16.7%sy,  0.0%ni, 73.3%id,  3.3%wa,  0.0%hi,  0.0%si, 
0.0%st
Mem:   7920416k total,  5041248k used,  2879168k free,   334336k buffers
Swap:  8124412k total,      172k used,  8124240k free,  2766816k cached

   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND 

  1810 root      20   0  301m 194m  24m S   27  2.5  14:43.91 Xorg 

     6 root      RT   0     0    0    0 S   23  0.0   0:17.39 
migration/0
     8 root      RT   0     0    0    0 S   13  0.0   0:40.38 
migration/1
    17 root      RT   0     0    0    0 S   12  0.0   0:32.61 
migration/3
  2338 jfb       20   0 1365m 255m  48m S    9  3.3  19:46.92 compiz 

    13 root      RT   0     0    0    0 S    5  0.0   0:31.98 
migration/2
  9789 root      20   0     0    0    0 S    5  0.0   0:02.17 
kworker/3:2
10189 jfb       20   0  510m  16m  10m S    2  0.2   0:01.11 
gnome-terminal
  1373 mongodb   20   0  341m  38m 8844 S    1  0.5   3:18.10 mongod 

10008 root      20   0     0    0    0 S    1  0.0   0:01.23 kworker/0:0 

  2151 jfb       20   0 25544 2596  572 S    0  0.0   1:14.42 
dbus-daemon
  2433 jfb       20   0  590m  19m  10m S    0  0.3   3:06.79 
unity-panel-ser
  9788 root      20   0     0    0    0 S    0  0.0   0:00.44 
kworker/2:1
     1 root      20   0 24440 2352 1276 S    0  0.0   0:00.83 init 

     2 root      20   0     0    0    0 S    0  0.0   0:00.02 kthreadd 

     3 root      20   0     0    0    0 S    0  0.0   0:11.34 
ksoftirqd/0
     7 root      RT   0     0    0    0 S    0  0.0   0:00.39 watchdog/0 

    10 root      20   0     0    0    0 S    0  0.0   0:01.90 
ksoftirqd/1

I am curious as to what those entries for migration/xx are?

Thanks,  Jim