I recently found out a life-changing tip with Firefox. Right click any search box on any website and hit "Add keyword for this search." You can then assign a prefix which you can use in the address bar to search that site. For example, I have these set up:
Opera has had this feature forever, since around 2001. Long enough ago that it shipped with search keys for Altavista and Lycos along with Google. The feature was a primary reason I started using Opera in the first place.
Originally you had to dive into a config file to add non-default search providers, but it's now in the UI just like Firefox, right click any text field and select "Create Search".
Search YouTube: tube <query>
Search Urban Dictionary: urban <query>
Search Amazon: amazon <query>
Search Wikipedia: wiki <query>