Well... as Corker said, with such a fast rapid release cycle, there are bound to have some incompatibilities with add-ons or extensions and that too, when we jump to install it even 1 day before the browser is officially released. (I am talking about the Firefox 7 here which was yet to be released officially when we downloaded the installer from Mozilla FTP).

This rapid release cycle has got its own advantages and disadvantages. The incompatibility is one of them.