Strange things can happen. In the process of accepting a firm offer listed on the website and told during the interview process it was "very" firm, I asked to have my evaluation time period shortened (Which is when I would be eligible for a raise.), so they decided to just increase the salary.
Find out if you really want this job. Review everything in the compensation package. You may be able to get more paid holidays, flexible scheduling, etc. or they may just offer more.
I don't recommend going into this process thinking you can just ask for a larger salary at a later point unless you are really basing it on other assumptions like you assumed it included a 401k or other retirement plan. Since it does not, you would need a larger salary to compensate.