Fix cut off text in Global Search in Firefox

Summary: Fixes T7914. Firefox is a special browser with special needs.

Test Plan: On Mac, test Safari, Chrome, Firefox. On Windows, IE and Firefox.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7914

Differential Revision: https://secure.phabricator.com/D12611