The new version of Screengrab! is pretty light on the requirements.

The basic requirements are:

  • Firefox 2.0+

That will get you going with the Canvas implementation using toDataUrl.

If you want to use the Java implementation (and thus, capture the occasional Flash image) you will also need:

  • Java plugin 1.3+
  • (Mac users only) Java Embedding Plugin

As of Firefox 1.5, the Java Embedding Plugin is bundled with Mac installers, so forget that second requirement. It’s just there for completeness.