ConQuery is a Firefox extension with configurable context-search capabilities.
This is a plugin for the extension that allows me to select text in a Firefox window and search Wikipedia with that text. To install the plugin, paste this into a text file with the file extension ".cqr" in ConQuery's searchplugins directory in your Firefox profile's directory.
#Status: Working Full
# ConQuery plugin
# by User:Saxifrage @ English Wikipedia
#
# Language: en
#
# Created: January 12, 2006
# Last updated: (first release)
#
# Known issues: none known
#
<SEARCH
name="Wikipedia (en)"
description="Search English Wikipedia"
action="http://en.wikipedia.org/wiki/Special:Search"
category="web search"
method="GET"
>
<input name="search" value="[:selection]">
<input name="go" value="Go">
</search>