On Windows box, I usually grab web pages screenshot using Fireshot add-on for Firefox. It got rich features, including built-in editor, annotation insertion, printing and e-mail integration. Too bad it’s not available for Linux.
Anyway, there’s still plenty of screenshot add-on available for Linux. Currently I’m using Screengrab. It simply saves webpages as images or copy them into clipboard. It can grab complete page, visible portion or just a selection. It also integrated to Firefox context menu.
Taking screenshot with screengrab
Well, it’s not as sophisticated as Fireshot, but it’s good enough for my need 
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