The OP specifically said "after" the big anniversary update. So doing a search for similar posts really isn't the way as this particular anniversary update has done A LOT of changes under the hood....

Im a little lost here, Firefox 64bit has been out and supported for a long time now....Been using it for a long time now even before Windows 10 and the 64bit FF has been fine since the launch of...

There is a way to still completly stop it in the process area. Like you said, it pops back too quickly but i found a way to stop it but you gotta be a bit quick but the way i did it gives you enough...