Note that this thread discusses the "I actually want to scroll to the top" use case, which might take a while for long pages. People in that estimate that this is a Common Thing you want to do.
The GP complains about being _required_ to scroll to the top to reach the address bar/the tabs, which is plain wrong (but might be a case of bad discoverability?).
https://groups.google.com/forum/#!topic/mozilla.dev.gaia/QP7...