With Firefox OS 2.5 (which is quite young!), it is possible. However, those addons need to be specifically designed for FxOS. There is no AdBlocker at the moment, but I am sure it is on many peoples wishlist. In a few weeks time there will be one available, I'm sure :)

Oh, and in the mean time you can use permanent private browsing mode with tracking protection. That works just like an AdBlocker!

Thank you! And what is the best method for searching for FxOS 2.5 browser add-ons? The Marketplace's add-on section seems to just contain OS add-ons.