Mozilla has set loose Firefox 10, the latest version of its open-source Web browser for Windows, Mac OS X, and Linux. New features in the release are largely limited to technologies aimed at Web developers, but there’s one important new feature that ought to appeal to anyone who has augmented their browser’s functionality: by default, most add-ons will be compatible with new versions of Firefox by default, and users will have an easier time managing and (if necessary) updating their add-ons to new versions of the browser. In previous versions of Firefox, Mozilla assumed add-ons weren’t compatible with new versions...