On an older computer I’ve had problems with Adobe Flash based videos flickering – the effect is like the video image shrinking to the top-left (about 25% to 33% of the original size) and then popping back down. The video plays without frames dropping but each video flickers along like this once every few seconds. Here are two solutions to that bug/issue.
This fixes flickering flash videos (like on YouTube) for me in both Opera 10 and FF3 – either:
If you don’t want to manually append that string on the end of your video then you can use Greasemonkey (for Firefox) to do it automatically. Some scripts are available for that but I’ve not tested any as yet (I don’t use YouTube that often).
Note that &fmt=18 (and &fmt=6 or just &fmt) is a HD mode and so this fix may not be good for you if you are on dial-up or any low-bandwidth connection.
An example link with the video flickering fix.