For some reason when I read answers now they are ordered by time of submission rather than by votes (which was my default setting until recently, apparently).
How do I return to the ordering by votes?
The user-interfaces offers three options to order the answers: "active", "oldest", "votes." You can make this selection via a tab, on the right at the top of all answers. You can see it here, too.
This choice is "sticky", that is if you change it for one thread, this choice is recorded as your choice and used for all threads on the site (meta and main are separate sites, though).
Thus, to return to the situation that answers are ordered by "votes" it will suffice to select the respective tab the next time you browse a thread on main (assuming the request concerns main, otherwise you can change it right here).