resolve #1314 and #1650 -- firefox fixed their flexbox performance issues
resolve #1314 and #1650 -- firefox fixed their flexbox performance issues

tscholl2/smc,sagemathinc/smc,DrXyzzy/smc,tscholl2/smc,tscholl2/smc,tscholl2/smc,sagemathinc/smc,sagemathinc/smc,DrXyzzy/smc,sagemathinc/smc,DrXyzzy/smc,DrXyzzy/smc,tscholl2/smc