Revert Site lets you get the old Facebook design / layout back for Group pages, Fan/Business Pages, Event pages and certain other pages too. It cannot revert the Newsfeed or Personal profile pages, and you will see those in the new design, but when you visit a Group page, you should automatically see it in the old style design. For business/fan Pages, or event pages, you may need to reload the page or open it in a new tab in order to see them in the old style layout/design.
Revert Site is very quick to install, and very easy to use, it just has two options, On and Off. It is turned on by default when you first install it.
If you wish to temporarily disable Revert Site, you can easily do so by clicking the extension icon, in the browser's extensions toolbar, then setting the Revert mode to "Off". To turn it back on, just select "On".
If you can't find the Revert Site (R) button in your extension's toolbar, it may be hidden behind the "Wireframe cube" button, so click that and see if its behind there.
Revert Site can currently only revert certain pages to the old design (Pages, Photo album edit pages) most other pages will load in the new design.
Revert Site won't work if you open Facebook via the Speed Dial button on Opera's new tab page. If you do open Facebook via the speed dial button, quickly click in the URL/Address bar and press return, then Revert Site should run ok. Otherwise if you open Facebook via a bookmark or by typing the URL in (fb.com works) then Revert Site should run ok too.
If you have any problems with video and voice Messaging on the Facebook site, with this extension installed, again using the auxiliary Facebook messaging website, messenger.com to do your Facebook video and voice calls should work fine.