Gmail – Does Gmail use Flash

While it isn't a flash, you might try enabling the Gmail Labs "Title Tweaks" item. It will make it very easy for you to spot your unread email count on the tab's title. This is basically how I accomplish what you're after.

As for chat, it seems like sometimes it will update the title as well but I've noticed that doesn't always happen. I don't have a great solution there.

I'm not sure about Flash, but I recognize the problem you're having. Firefox's <video> support hasn't yet been done properly, so it's much slower than any other method.

If nobody else suggests something you like better, FlashVideoReplacer would let you swap out the YouTube-provided player for either the Quicktime or VLC plugin and both should run faster than Flash or Firefox's internal <video> support.

(It also supports various players which appear in their own windows, but you probably don't want that)

Another option you could try would be to track down WHY YouTube is forcing HTML5 on Firefox by trying these one-by-one:

• deleting all YouTube cookies (YouTube's fault but configurable)
• running in Safe Mode to disable extensions (One of your extensions' fault)
• using the User Agent Switcher extension (YouTube's fault, not intended to be configurable)

Finally, if none of that works, you could give Google Chrome a try. Its extension system isn't as powerful as Firefox's, but AdBlock Plus does have a version for it.