If you still don’t know Firefox Panorama keyboard shortcut changed new one is Ctrl + E for windows and Cmd + E in Mac and Linux. I don’t think shortcut will not be changed again. If any webpage that intercepts  Firefox from opening Panorama with Ctrl + E shortcut then you can use Force Panorama Shortcut which makes Panorama Shortcut(Ctrl/cmd +e) work even if a webpage or web app intercepts from using it.

Force Panorama Shortcut makes Panorama shortcut to work in all situations.

Force Panorama Shortcut works with Firefox 4.0 beta 7  and nightly builds of Firefox 4.