Volkside design company made a gift to web developers by releasing a free bookmarklet
Wirify , with which you can display the wireframe of any site with one click. It is a useful thing to quickly evaluate some aspects of website design: a modular layout system, visual hierarchy, free space, symmetry, golden ratio, rule of thirds, etc.
You can drag the bookmarklet to your bookmarks and launch it on any page, it works with all modern browsers.
Rendering on jQuery does not always work perfectly, sometimes slight distortions happen. Exporting a frame from Wirify is not supported, but you can use plugins to save a web page as a picture:
Screengrab for Firefox or

Screen Capture for Chrome.
If you have to deal with wireframes at work, it makes sense to look at other tools as well. For example, the developers of the
jMockups web service promise in the near future to roll out the feature of importing the frame of any site in a couple of mouse clicks. That is, you can just borrow and borrow someone else's layout for your project without copyright infringement. By the way, for Wirify now they also make an
export feature to the
OmniGraffle program (an analogue of MS Visio for Mac OS X and iPad).