Firefox version: 16.0.2
Operating system: Mac OS X 10.8.2
From website: https://addons.mozilla.org/en-US/firefox/addon/firebug/
Date: 11 Decemeber, 2012, 11:30am CET (10:30am UTC)
The headline advertises Firebug version 1.11.0. The link from the download button goes to https://addons.mozilla.org/firefox/downloads/file/123595/firebug-1.7.3-fx.xpi?src=dp-btn-primary and the install is of version 1.7.3, which does not work in FF16.
Installing a specific version from https://addons.mozilla.org/en-US/firefox/addon/firebug/versions/ got things working for me, but the link should really be fixed.