Adobe Flash (formerly Macromedia Flash) is a propietary multimedia platform used mostly to display advertisements with creepy tracking on web pages. The majority of users install it to view video and simple games on web pages.
 Flash on Linux
Adobe Flash for GNU/Linux has typically worked extremely poorly. It is basically a buggy pile of security risks.
Version 18.104.22.168+ of adobe flash seems to work nicely on both 32bit and 64bit systems.
 Icecat 6
Icecat version 6 just hangs for ages when you visit a page with a flash object on it. You can fix this by visiting about:config. Right-click and select New and Boolean. Add preference name dom.ipc.plugins.enabled.libflashplayer.so and set it to false. You can alternatively set dom.ipc.plugins.enabled to false (same effect, but applies to all plugins). This appears to be a Icecat only bug, Firefox 6 + flash works like expected.
Icecat 6 also has problems with non-evil flash players like gnash and lightspark, these can also be fixed using the same trick. Add these as boolean values and set them to false:
 Firefox / Icecat hangs after return from suspend to RAM/disk
Adobe flash version 22.214.171.124_rc201109061 makes Firefox hang after returning from suspend and resume on both 32bit and 64bit systems.
Searching the Internet reveals that the garbage Adobe piece of trash software also hangs Windows computers returning from suspend.
A solution is to use adobe-flash version 10.3.183.10 (or 10.x) instead of 11.x as this does not happen with that version of flash.
Running a flash video in Firefox/Icecat uses far less CPU than running flash in the Chromium browser.