apply Uint8Array speed optimization in Firefox
apply Uint8Array speed optimization in Firefox

In Firefox the buffer is not `instanceof Uint8Array` so let’s use
Buffer.isBuffer instead

loon3/buffer,nolanlawson/buffer,beni55/buffer,btd/buffer,LinusU/buffer,kawanet/buffer,loon3/buffer,kawanet/buffer,nolanlawson/buffer,LiuDeng/buffer,SAGV/buffer,SAGV/buffer,mafintosh/buffer,LiuDeng/buffer,feross/buffer,feross/buffer,feross/buffer,substack/native-buffer-browserify,jessetane/buffer,mafintosh/buffer,btd/buffer,LinusU/buffer,beni55/buffer