-moz-window-inactive + feGaussianBlur
Applies Gaussian blur to the window when it's inactive. (Firefox 4 only)
by marcoos
HTML
<h1>-moz-window-inactive + feGaussianBlur</h1>
<p>Deactivate this window for its content to get blurred - even while playing YouTube video.</p>
<iframe title="YouTube video player" class="youtube-player" width="480" height="390" src="http://www.youtube.com/embed/g0owAXCPPnc?autoplay=1"></iframe>
<p>No JS here. Flash is only used by YouTube video above.</p>
<p><small>Note: -moz-window-inactive and using SVG filters for non-SVG content is non-standard yet.</small></p>
<footer><small>Another HTML5+CSS+SVG experiment by <a href="http://twitter.com/marcoos" target="_blank">@marcoos</a>.</small></footer>
<svg width="0" height="0">
<filter id="f1"><feGaussianBlur stdDeviation="3"/></filter>
</svg>
CSS
body { font-family: lucida grande; }
body:-moz-window-inactive { filter: url(#f1); }
h1{font-size:24px}
p {margin:0.5em 0}
iframe {border:0}