R1:98a62c9e4998

Fix firefox float bug in Conphernce menu

Summary: These floats were wonky in FF, adding some hardening to make sure they clear.

Test Plan:
Firefox, Chrome, IE.

{F1815981}

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D16547