I had this problem and solved it! All you have to do is follow this guide to change the default search engine back to Google.
Follow these instructions:
1.2Type in about:config in the address bar.
2. Then type in search in the Filter bar..
3. Modify the browser.search.defaultenginename property to Google. and then modify the browser.search.defaulturl to “http://www.google.com/search?lr=&ie=UTF-8&oe=UTF-8&q=” without quotes.

Some guy that wrote how to do this

guysoft is almost correct, but he's linked to a site dating from 2006. Since then Firefox values have changed and what you need to do now is as follows:

• In the location bar, type about:config and hit Enter.
• In the filter at the top, type: keyword.URL
• Double click it and remove whatever's in there and replace it with http://www.google.com/search?q=
• Go to File | Exit
• Restart Firefox, go to the site you want to set as your homepage.
• Go to Tools | Options | General.
• Make sure it says "Show My Homepage" in the first dropdown menu.
• Click the button called "Use Current Pages" to set the homepage to the one you have on the screen.

The URL to add in "keyword.URL" becomes a link in this post, so right click it and choose "Copy Link Location" to copy it to the Windows clipboard. Then hit CTRL+V to paste it. Saves you having to type the whole thing.

Thanks for your help (the both of you). The problem is almost solved. If i type wikipedia on the bar, it sends me to the google results for "wikipedia," and not the actual wikipedia page. And while this is a lot better than before, id still like the awesome bare to work as it did, i.e. send me to the wikipedia website whenever i type wikipedia, or better yet send me dirctly to the wikipedia entry for star wars when i type in "star wars wikipedia". Thanks!

To load Wikipedia, type it in the address bar and hit CTRL+SHIFT+Enter. Works for any .org

To load a .net, press SHIFT+Enter after you type the name of the site.

And for a .com, press CTRL+Enter.

thanks Xircal, i knew that, but what i meant was that firefox used to recognize that i was searching for the wikipedia website when i typed the word "wikipedia," (no need for .org or anything) and it sent me to the website directly, instead of the google results for wikipedia as it does now.

Please see this article: http://www.businessinsider.com/how-to-use-the-location-bar-aka-awesome-bar-to-search-the-internet-faster-in-firefox-4-2011-4

Thanks Xircal! Problem solved

You're welcome.