I use flash with firefox with no problems. It can cause problems but there are some sites you can't use without flash.

Get flash here see link.

Here is a link that might be useful: Flashplayer 9.0

Thanks..pm2

Even with Flash, I think there may be some sites that won't work right in FireFox. For them, FireFox has an extension (aka add-on) called IE View, which I like very much. You can right click and chose "View in IE" from the menu and that particular site will open up right IE while you still have FF open, and then videos and other things such as recalcitrant "submit" buttons and the like will work fine.

I am using the original IE View developed by Paul Roub, but it is hard to find at the Extensions site. If you search for IE View, it is on page 5 of the results, so I'll give the URL here.

There is also an extension called IE View Lite, which is supposed to have the same features and take less space. Just now I also found something called IE Tab, which looks useful, but I haven't used it yet.
Here is the URL for IE Tab.
https://addons.mozilla.org/en-US/firefox/addon/1419

URL for IE View Lite:
https://addons.mozilla.org/en-US/firefox/addon/1429

Here is a link that might be useful: IE View (the original one by Paul Roub)