Lb stands for level break. This means there was at least one ambrosia spent on the unit to raise its level cap. Usually sellers would say what that cap is: e.g. selling 124/126 Dolce (currently level 124, but its level cap has been raised to 126). MLB means max level cap, which is the usual level for the card +20.
As far as I know, firesale just means a sale with huge discounts lol. Often times, the prices will be pretty cheap, but the sellers may want pure TE offers only.