GNOME Shell to support a "classic" mode

you may want to notice that the chrome extensions API doesn't allow some things to be done that are done in firefox (this is one of the reasons noscript doesn't exist for chrome)

Firefox also has an extensions API, and things that use that are very stable. But Firefox didn't start with an explicit API, instead extensions are allowed to muck with anything in the browser, and ones that do are extremely sensitive to any changes in the browser (potentially including compile options)

as in everything, there are tradeoffs