Comment 18 for bug 225165

I experience this too since I'm on Ubuntu (Ubuntu 10.10 with each current Firefox / Adobe Flash version)
I'm using the Flash-Aid plugin for FF and it doesn't make a difference whether I use Adobe stable or Beta version of flash.
In the past I've tried each "solution" I've found in the net (without success) for this problem and I'm really annoyed about it...

This URL can be used as reference, I've here a cpu load of 60-89% on a dual core cpu (T61 Intel® Core™2 Duo CPU T7800 @ 2.60GHz × 2 with 4 GB RAM)
often firefox freezes here (app not responding, greyed out)
http://www.gaiaonline.com/tank/11998771/?gsiUrl=www&userEnvironmentId=1237135&version=133&quality=low&location=popUp&isInEdit=false&graphicsServer=http%3A%2F%2Fs.cdn.gaiaonline.com%2Fimages%2FGaia_Flash%2Faquarium%2F

using the same URL on the same machine with windows XP, Firefox 13 and all plugins listed below runs smooth and doesn't bring the cpu's above 30%

Currently I'm running Ubuntu Version 12.04 (precise) (32-Bit), Kernel Linux 3.2.0-25-generic-pae,
with Unity, compiz,

Firefox 13.0 (but it happens in the same way if all plugins and add-ons are disabled except flash)

with the following enabled plugins:
Windows Media Player Plug-in 10 (compatible; Totem)
The Totem 3.0.1 plugin handles video and audio streams.

IcedTea-Web Plugin (using IcedTea-Web 1.2 (1.2-2ubuntu1))
The IcedTea-Web Plugin executes Java applets.

IcedTea-Web Plugin (using IcedTea-Web 1.1.3 (1.1.3-1ubuntu1.1))
The IcedTea-Web Plugin executes Java applets.

QuickTime Plug-in 7.6.6
The Totem 3.0.1 plugin handles video and audio streams.

DivX® Web Player
DivX Web Player version 1.4.0.233

VLC Multimedia Plugin (compatible Totem 3.0.1)
The Totem 3.0.1 plugin handles video and audio streams.

Shockwave Flash
Shockwave Flash 11.2 r202 11.2.202.0

iTunes Application Detector
This plug-in detects the presence of iTunes when opening iTunes Store URLs in a web page with Firefox.

Gnome Shell Integration
This plugin provides integration with Gnome Shell for live extension enabling and disabling. It can be used only by extensions.gnome.org

and these active addons:
Adblock plus 2.0.3
better privacy 1.68
flash-aid 2.2.3
flashblock 1.5.15.1
ghostery 2.7.2
tab mix plus 0.4.0.2

top without flash:

georg@LinMob:~$ top

top - 20:24:37 up 4:09, 2 users, load average: 0.49, 1.00, 1.37
Tasks: 171 total, 1 running, 170 sleeping, 0 stopped, 0 zombie
Cpu(s): 7.7%us, 3.0%sy, 0.0%ni, 89.3%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 4055644k total, 1967232k used, 2088412k free, 126620k buffers
Swap: 10239996k total, 0k used, 10239996k free, 1093980k cached

  PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
 1733 georg 20 0 425m 201m 37m S 7 5.1 27:04.72 compiz
 1917 georg 20 0 157m 23m 12m S 3 0.6 8:08.14 unity-panel-ser
 1850 georg 20 0 147m 11m 8664 S 2 0.3 4:25.36 indicator-multi
 1919 georg 20 0 65808 7060 3520 S 2 0.2 3:57.25 hud-service
 2521 georg 20 0 586m 118m 33m S 2 3.0 9:27.87 firefox
 1035 root 20 0 150m 132m 12m S 1 3.3 22:32.42 Xorg
 1940 georg 20 0 62040 5024 3644 S 1 0.1 1:46.84 indicator-appli
 2317 georg 20 0 179m 14m 10m S 1 0.4 1:22.90 psensor
 1705 georg 20 0 7464 3668 628 S 1 0.1 2:03.93 dbus-daemon
  873 root 20 0 32672 5152 4316 S 0 0.1 0:02.05 NetworkManager
 1025 root 20 0 3584 644 496 S 0 0.0 0:02.44 irqbalance

top with flash from the above URL with all FF plugins disabled:

georg@LinMob:~$ top

top - 20:25:58 up 4:10, 2 users, load average: 0.96, 1.00, 1.34
Tasks: 173 total, 2 running, 171 sleeping, 0 stopped, 0 zombie
Cpu(s): 49.2%us, 8.9%sy, 0.0%ni, 41.5%id, 0.5%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 4055644k total, 2005444k used, 2050200k free, 126732k buffers
Swap: 10239996k total, 0k used, 10239996k free, 1095696k cached

  PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
 3731 georg 20 0 259m 56m 20m R 83 1.4 0:14.07 plugin-containe
 1733 georg 20 0 425m 201m 37m S 16 5.1 27:15.27 compiz
 1035 root 20 0 151m 133m 13m S 9 3.4 22:44.46 Xorg
 1917 georg 20 0 157m 23m 12m S 3 0.6 8:10.82 unity-panel-ser
 1919 georg 20 0 65808 7060 3520 S 1 0.2 3:58.49 hud-service
 1747 georg 9 -11 163m 6524 4524 S 1 0.2 0:51.07 pulseaudio
 1705 georg 20 0 7464 3668 628 S 1 0.1 2:04.71 dbus-daemon
 1850 georg 20 0 147m 11m 8664 S 1 0.3 4:26.67 indicator-multi
 1940 georg 20 0 62040 5024 3644 S 1 0.1 1:47.46 indicator-appli

see also attached screenshots of my sysmon