It appears that at some point in the recent (distant? I don't know) past, Memory Alpha changed its domain from
memory-alpha.fandom.com. Given the copious number of times links to that site appear in questions and answers on SciFi.SE, is it possible to fix them all with some kind of global find/replace?
I am assuming that "wikia" has changed its name to "fandom".
wikia.com is successfully redirecting to
fandom.com so I don't know why the MA URLs aren't.