How to create a 1280x800 screenshot of a Chrome Browser viewport

Question

The Chrome Webstore requires screenshots of the exact size 1280x800.

Using the system-built-in screenshotter, I have often failed by a few pixels, which required tedious image cropping by hand or the convert tool.

How are those easily created?

Answer 1

The old answer no longer works for chrome-extension:// pages. On systems that support it like Ubuntu, you can use the Shutter app. On OS X, the shutter project mentions the skitch app.

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An easy way to do this is install Window Resizer and Fireshot.

Answer 2

With Firefox, this is real easy:

Menu -> Developer -> Responsive Design Mode (Ctrl-Shift-M)

gives you a drop-down to select the window size. There is also a button to create a Screenshot at this exact size.