Rufnex

FullscreenWidth is a very simple Plugin, that adds a input field to change the editarea width, next to the toolbar buttons at the fullscreen view.
The standard width of the WordPress editarea is 647px, for some reasons this was to small for me. FullscreenWidth let you change the desired width on the fly by simply type widith in the input box. Afer you click elsewhere on the screen the width of the editarea is changed.
Note: The width is set as long you dont reload the browser.

FullscreenWidth

FullscreenWidth adds a input field to change the editarea width, next to the toolbar buttons at the fullscreen view.

jordesign

=Preview your site at random page widths to test your Responsive design.=
WP Responsive Preview provides an additional previewing options for your site. Loading a Responsive Preview will load the page in a flexible framework at a random width, helping you see how your page looks at different widths. It also lets you re-randomise the width quickly, to test multiple widths.
This plugin is based entirley on [ish. from Brad Frost][http://bradfrostweb.com/demo/ish/] – a great standalone tool for previewing your site at random widths. His post does the best job of explaining the reasoning behind ish. (and therefore WP Responsive Preview).
“The real reasons for this tool is to educate and to facilitate a mental shift. Many clients, designers and developers get hung up on specific device widths, which is why this tool doesn’t include any such language, device chrome or anything like that. Ish. helps keep everyone focused on making a design that looks and functions great at any resolution.”

WordPress Responsive Preview

Preview your site at random page widths to test your Responsive design.

FullscreenWidth vs WordPress Responsive Preview