I suspect that both are right. Some people are having issues and others are not. I don't seem to have any lag at all when typing even with multi megabyte size

I suspect that both are right. Some people are having issues and others are not. I don't seem to have any lag at all when typing even with multi megabyte size files. Maybe you could give some more details into exactly what actions were slow for you and what types of files you were editing. Actually, thanks to innovations in Mozilla's servo, the web may actually become faster than native.