The Simpsons has always made it obvious that they ingore continuity totally. It's part of the "in joke" that they occasionally reference.
Assume you meant "ignore"---don't think they're goring the concept. ;-)
As I stated before, not (completely) true that it's ignored *totally*---a complete lack of continuity would make it "The Far Side" or "Looney Tunes". Last I checked, Maude's still dead and Apu still has those 87 (or whatever) kids... ;-)
Do think it fits the "sitcom continuity attitude" mold, though---i.e., self-contained stories that generally don't refer back to previous episodes...except that the "Simpsons" does do that on occasion (the various Sideshow Bob episodes for one, or the episodes with Homer's half-brother Herb). (Though like I said, my sentiments are based on the first 8 or 9 seasons' episodes, before I stopped watching...not wasting brain cells pondering any of the 2000s-era episodes I've heard about... :-p ).
As for Final Crisis, I suspect is will not eliminate the 52 earths as some want to believe or expand them to infinite earths. Instead, my opinion is that it will be the final crisis for one of these earths, probably Earth 1, which I think will be revealed as the Silver Age DC Earth.