The emulator was written by Software Engineering student Grant Galitz. Like most browser games, it doesn’t need you to install anything on your computer. It even has built-in games! You can also load .gb or .gbc files, although I wasn’t able to test that. I also don’t know how the emulator handles game saves.
Technically the emulator can run even on mobile browsers, but it was slow and unplayable on my iPad 2. Perhaps newer devices will fare better. Check out the emulator on Grant’s website before Nintendo falcon punches it down. You can also check out its source code at GitHub.