Easyjet at certain airports (certainly at NCE) uses the jetway to board the front door for rows 1-15 and sends the others down stairs to board the back door. Fortunately it doesn't rain that often in Nice, but I've done this several times and it's a remarkably slick operation. Same for disembarking. They also do the boarding pass scan whilst incoming passengers disembark and leave the passengers in a holding area (not very pleasant).