Fix tests on Firefox.
Fix tests on Firefox.

msalsbery/openseadragon,jmnetus/openseadragon,openseadragon/openseadragon,seanich/openseadragon,jmnetus/openseadragon,avandecreme/openseadragon,seanich/openseadragon,LarissaSmith/openseadragon,rdlester/openseadragon,LarissaSmith/openseadragon,msalsbery/openseadragon,rdlester/openseadragon,openseadragon/openseadragon,avandecreme/openseadragon