Seamonkey

I have been using Seamonkey as my main browser for several years, after a tip from someone on TR. Lately there have been increasing instances of sites failing to work with it. Chase, the bank, simply refuses any log-in on a browser not in its short list, while Ally Bank fails to accept log-in on this browser. Similarly, The Economist newspaper too fails to accept log-in, as does the Safeway grocer customer site. Does anyone know what is happening?