I'm moving these here, from the project page where I originally listed them. Feel free to edit this to add any you find.
- No endorsement of a particular extension is implied.
Browser extensions/addons that show mouseover popups within Wikipedia
- wikipedia plus
- wikipedia quick hints
- wikipedia smart links
- wiki it
- LiveWiki (github)
- wikipedia peek
- wikipeeks for wikipedia
Browser extensions/addons that show Wikipedia/Wiktionary content at any external site