There are 3 or 4 cations that trigger a browser. You'd hagve to ckick Always for each one to get it no never ask again.
If it's the same action cauing it every time (say clicking a link in an email), there's a problem with the phone. Hope the tech people at your carrier's store are good, because if they aren't you're just going to have to learn to live with it. (It can be caused by different things in different phones. My "new" refurb is going back on Monday because it sometimes forgets which is the default launcher and, to me, "almost as good as" isn't the same thing as "same or better".)