You have to ask yourself what is more important to you having to do couple option changes, but keeping the browser up to date and secure or having sane(r) defaults, but lacking behind in security updates.

Yes, I'm sure the author does their best, but I doubt this is their day job. Meaning if there is an update during working hours he might not get to update his fork until several hours later or if he is on vacation it might be days or weeks. What happens when he abandons the project? Usually the fork projects wind down after some time and there is no indication for the users that they are using abandonware with God knows how many missing security patches.

Of course there is ideal world where we wouldn't have to make these choices, but at least I am going to stick with Firefox until something actually bad happens.