Imagus - The extension is intended to complement image features that (I think) is missing from Opera by...

globalquiz.org - Difficult, multiplayer and multi-language trivia game.

Image Max URL - Help find larger or original versions of images, including a customizable image popup feature

The Quizopedia - The Quizopedia is a top-notch quiz-based application that provides the overall development of the interesting candidates by offering interesting quizzes focused on enhancing analytical, reasoning, and decision-making skills.

Thumbnail Zoom Plus - The official site of the Thumbnail Zoom Plus add-on for Firefox

HugeQuiz - test your knowledge with a variety of quizzes about everything.