Firefox allows the use of so called "smart bookmarks".
With smart bookmarks you can make a bookmark, specify a placeholder and a keyword.
You can now type the keyword with a query string in the address bar and then...magic
Example:
The %s will be abbriviated with the specified query string.
With this example you can type bts $package in the address line and firefox will load:
http://bugs.debian.org/$package
Another usefull example is:
http://en.wikipedia.org/wiki/%s
This will query wikipedia and will go to the description page.
For search queries there is also the nice plugin
ConQuery.