I wondered about the rubber cover on mine too. I didn't really look at it, and tossed it on the tank. It made it feel like a push in, on/off thing. I finally figured it out. And took the cover off.
Then my brother got his going, and used the brackets(legs) on his. You have to remove the rubber to get those on.
Drs.F&S is known as Dr's or Fosters around this house. ; )
I've done alot of ordering from them over the years. With very very few problems. And those were always taken care of very easily, with 1 phone call. And if your trying to figure something out about a product and the person answering the phone can't answer it. They'll transfer you to a tech person, to see if they can help.
They've got to be selling the Cr*p out of those Coral Life lights. The one I just ordered for my moms 55g tues. should be here tomarrow. That makes 2- 48" and 1 - 36" fixture to this house in a month. They're almost always on back order.
My order Tues. morning(when I saw the 48" In Stock) was over $200. That included 3 - 25lb bags of gravel. And was only $19.99 Shipping.

From the looks of the tracking. Everything but the gravel should be here today or tomarrow. And the gravel might be tues.
I just thought about the Nitrate Test kit. That could be one of the slow deliveries. My last order with test kits in it had to go ground, and took a few days to get here.