The "Get Add-ons" view in Firefox is an iframe to a page hosted by addons.mozilla.org. AMO, as all Mozilla sites, use GA to collect aggregate visitor statistics. We negotiated a special contract with Google [1] to only collect a subset of data and that that data is only used for statistical purposes.
Google Analytics is only loaded when this view is loaded, and is not otherwise "inside" Firefox. I filed an issue [2] to make sure that our privacy policy is linked from the Get Add-ons view so users can be better informed.
Mozilla tries to walk a very thin wire to ensure that we have the data we need to make sure our products are working properly without being intrusive, and to let concerned users opt-out of even that baseline data collection.
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=697436#c14 [2] https://github.com/mozilla/addons-frontend/issues/2789