Surfing Waves

I bought a Firewire Addvance 7 ft a while ago, but I find it often slips out of my grip when I try to duck dive it , or duck dip really
as it has a fair amount of volume and doesn't sink easily.
Is it frowned upon to wax the underneath sections of board and along the rails where my hands need the most grip?

I don't know but I used to wax the rails and top area where I grab my board for duck dives. My current boards only allow duck dips an I haven't had that problem but try to wax that area anyway but only on the top. Wax on the bottom of the board will cause drag and may slightly affect the performance of the board. If you are a beginner you probably won't notice

Go for it. I wax the nose/rails of my boards (top and bottom of rails) where I grip them for turtle rolls, and also where I tend to place my hands for popping up (since I sometimes grab the rails in a very bad habit...). Indeed, without the wax I think your abilities to turtle roll etc are significantly reduced

If you dont like the look/thought of wax in these areas, you can buy stuff like versa grip and put it on. But wax is fine.

(well, i guess I would say 'wax is fine' since i do it myself! but at least you know there is one other surfer in the world that does it)

Yes I also wax the nose rails on all my boards for grip, but only the topside. I have the same problem duckdiving my Addvance 6'6" in bigger waves. It's the thickness of the rails that makes you can't keep a good grip combined with the power needed to control such a high volume board in bigger whitewater.

Also, wipe off al the sunblock from your palms if you usually don't.

I don't. Haven't had a problem with grip so it is a non issue for me. I have big hand and work with my hands as well which might make a difference.