I was recently asked for a way to do this, and since I figured more people might like to know, here’s how:
Go to Tools => Web Developer => Developer Toolbar (check it), or simply press Shift+F2, then at the command line that appears in the bottom of the browser window, type “screenshot –fullpage” followed by an optional filename ending in .png.
A screenshot of the entire page will end up in your default downloads directory.
Here’s an example shot of the OmniOS installation guide:
