[octosphere]

It probably has something to do with (some) extensions not being very privacy friendly. Some extensions spy on the user in return for the utility the extension provides (remember the Stylish addon fiasco recently?). I'm not certain of the reasoning behind the decision. Also: it's possible to enumerate/detect what addons are installed in a browser with javascript (and thus fingerprint the user), although I think that bug was patched in Firefox and Chrome.