R1:e47b4f5b67e3

Fix "size=full" issue for images in Firefox

Summary: Fixes T8221.

Test Plan: {F410522}

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8221

Differential Revision: https://secure.phabricator.com/D12927