The quality of our daily life is getting more and more dependent on the quality of many important web applications running on the Internet. With the rapid evolutions of the web applications, effective maintenance techniques to guarantee the correctness of the evolutions are highly demanded. We present our initial work on exploring automated verification techniques for this purpose, via algebraic reasoning and model checking on the abstract navigational behavior of the evolving web applications expressed in labelled transition systems, against the desired properties expressed in temporal logic formulas combined with tree automata.