Having Firefox? CHECK.
Having a flash intensive site opened right now (Like YouTube)? CHECK.
Having the flash frame blinking repeatedly (even if no video playing in You Tube)? CHECK!
Well, if you answered all the above correctly, you have my sympathies. Because this pain in the butt problem has a small solution, which is not easily googled up in results.
Anyways, assuming you are having the browser up and running, fire up the Firefox add-ons window as below -
ALT+T for TOOLS > OPTIONS > GENERAL > MANAGE ADD ONS…
NOTE: The Geek shortcut – Ctrl + Shift + A will do the same stuff as above (you should have just the Firefox tabs open).
Ensure that you have selected the Plugins from the left options list (last option).
Scroll to the Shockwave Flash XXXXX entry, where XXXXX is your version of flash.
Now quickly hit disable. And Enable again. Check your flickering flash page (if the above solution has worked, you will have the issue resolved immediately).
You can go ahead thank me in the comments ;-)