While it is important to remain civil to all users, please remember that new users may not be familiar with Wikiquette. So if you encounter a mistake by a new user please do not bite the newbie.
This is an oldie but goodie, that for sure works in Firefox...
Visit Conveniently searching Wikipedia, and follow the instructions for your browser. It's a bookmarklet that sits on your toolbar, and which serves as a Wikipedia search button that you can activate from any web page. The next time you want to look something up on Wikipedia while browsing a web-page, highlight the term and then click on your new bookmarklet.