Fix Firefox getting started hang issue, fixes #1810
Fix Firefox getting started hang issue, fixes #1810

playi/pxt,switchinnovations/pxt,Microsoft/pxt,switchinnovations/pxt,Microsoft/pxt,switch-education/pxt,Microsoft/pxt,Microsoft/pxt,switch-education/pxt,Microsoft/pxt,switch-education/pxt,playi/pxt,switch-education/pxt,playi/pxt,switchinnovations/pxt,switchinnovations/pxt,playi/pxt,switch-education/pxt