fixes display of table header in FF
fixes display of table header in FF

elaOnMars/datawrapper,elaOnMars/datawrapper,ThuyNTran/datawrapper,kendrick-k/datawrapper,rubensfernando/datawrapper,rubensfernando/datawrapper,washingtonpost/datawrapper,devinit/datawrapper,kendrick-k/datawrapper,ThuyNTran/datawrapper,kendrick-k/datawrapper,grepman/datawrapper,motherjones/datawrapper,robmcloughlin/Insights,elaOnMars/datawrapper,qqming113/datawrapper,datafunk/datawrapper,rubensfernando/datawrapper,motherjones/datawrapper,ThuyNTran/datawrapper,datafunk/datawrapper,motherjones/datawrapper,devinit/datawrapper,devinit/datawrapper,ThuyNTran/datawrapper,devinit/datawrapper,washingtonpost/datawrapper,plusgut/datawrapper,grepman/datawrapper,robmcloughlin/Insights,washingtonpost/datawrapper,washingtonpost/datawrapper,qqming113/datawrapper,grepman/datawrapper,ThuyNTran/datawrapper,washingtonpost/datawrapper,rubensfernando/datawrapper,elaOnMars/datawrapper,washingtonpost/datawrapper,grepman/datawrapper,qqming113/datawrapper,plusgut/datawrapper,kendrick-k/datawrapper,datafunk/datawrapper,elaOnMars/datawrapper,grepman/datawrapper,devinit/datawrapper,ThuyNTran/datawrapper,grepman/datawrapper,motherjones/datawrapper,robmcloughlin/Insights,datafunk/datawrapper,robmcloughlin/Insights,kendrick-k/datawrapper,rubensfernando/datawrapper,datafunk/datawrapper,qqming113/datawrapper,robmcloughlin/Insights,qqming113/datawrapper,datafunk/datawrapper,plusgut/datawrapper,motherjones/datawrapper,kendrick-k/datawrapper,elaOnMars/datawrapper,qqming113/datawrapper,motherjones/datawrapper,devinit/datawrapper,plusgut/datawrapper