Name: Youtube Keyword: y URL: http://www.youtube.com/results?search_query=%s
Then just type "y civilization v" and shazam, you're on Youtube, looking at a list of trailers and previews for Civilization V.
Firefox has the same feature; I believe it's called "Keyword Search" and can be accessed through Bookmark Manager. I always found Firefox's separate search box redundant for this reason.
I actually use both. I've about 20 keywords - I use the search box when I think I'll need to search across multiple engines (though I usually copy paste the words, I guess I use them as a short scratch pad) and use keywords when I expect I won't have to re-enter the search elsewhere.
And for the keystroke-obsessed, Ctrl+K clears the location bar and puts in the question mark for you. :)
youtu+TAB and then enter your keyword. Works with every site that support opensearch. en.wiki+TAB will search wikipedia etc.
Chrome's extensions only have similar capabilities as Mozilla JetPacks have.
Link Widgets: https://addons.mozilla.org/en-US/firefox/addon/2933/
Basically, it studies the source for links like "next" and "previous," and lets you page forward and backward with alt+pageup/down. Works great on xkcd, New York Times, and many others.
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Noscript/Flashblock: 'nuff said.
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Colorzilla: http://www.colorzilla.com/firefox/
Color picker. Combined with Firebug, great for web dev.
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Leet key: https://addons.mozilla.org/en-US/firefox/addon/770/
Okay, this one I could live without, but the ability to rot13/hex/morse/octal/binary encode text at will is nice.
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Facepad: https://addons.mozilla.org/en-US/firefox/addon/8442/
I don't really use this one that often, but it's a good example of Firefox's superiority.
noscript: built-in, although configuration isn't that robust
flashblock: https://chrome.google.com/extensions/detail/gighmmpiobklfepj... https://chrome.google.com/extensions/detail/gofhjkjmkpinhpoi...
color picker: https://chrome.google.com/extensions/detail/egmjgagjcamhcilh...