fix test for firefox 49 (close #827) (#828)
fix test for firefox 49 (close #827) (#828)


georgiy-abbasov/testcafe-hammerhead,LavrovArtem/testcafe-hammerhead,DevExpress/testcafe-hammerhead,georgiy-abbasov/testcafe-hammerhead,miherlosev/testcafe-hammerhead,DevExpress/testcafe-hammerhead,miherlosev/testcafe-hammerhead,DevExpress/testcafe-hammerhead,AlexanderMoskovkin/testcafe-hammerhead,LavrovArtem/testcafe-hammerhead,DevExpress/testcafe-hammerhead,LavrovArtem/testcafe-hammerhead,churkin/testcafe-hammerhead,churkin/testcafe-hammerhead,miherlosev/testcafe-hammerhead,AlexanderMoskovkin/testcafe-hammerhead,miherlosev/testcafe-hammerhead,LavrovArtem/testcafe-hammerhead