Wikitab worked great under Mavericks, even worked under the first Yosemite public beta for awhile and then it just stopped. When it does work, it's the best. My only complaint was that it often skipped previous look-ups when I hit the back button.
Looks like a good idea for quick research if you don't use a MacBook with an already overcrowded menu bar. But since I'm a "rebel" who is still refusing the AppStore I'll have to open Wikipedia now and in the future in a browser window. Poor me. ;)