Firefox: BitmapData Handle?

I have heard that it is possible to get a bitmap/image handle of the webpage being viewed on a firefox browser. I ha开发者_如何学运维ve been researching for a bit and couldn't not find anything.

So I am hoping if anyone knows how to do this, preferable via the command line (bash, any other shell on Linux).

To be honest, any browser that I could do this on is fine as long as its simple and on the shell!

Thanks all

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Just one option: ImageMagick has an import command that will take a screenshot of any (X server) window from the command line. If you don't want the entire window you can specify a cropping area.