I do not think this is really much of a concern in practice. Nobody would bother to attack a browser that isn't popular (unless it is used by someone who is a t

I do not think this is really much of a concern in practice. Nobody would bother to attack a browser that isn't popular (unless it is used by someone who is a target themselves, but the attack wouldn't be for the browser but for the target and the chance of others being affected will be very very low) and by the time the browser becomes popular it will also have attracted a developer base and pairs of eyes large enough to have those bugs fixed. Remember the claims about Mac OS X security back in the early 2000s? Mac OS X wasn't secure because it had no security issues, it was secure because nobody bothered to attack it. As it became more popular (and it had to become very popular compared to what it used to be, which took several years by itself), it also attracted people attacking it. That would be the same story with a new browser. Or anything new and obscure for that matter.