I dunno. In favor, when used in this sense but without an explicit following prepositional phrase headed by of, is always elliptical, I think. "All those in favor (of the matter being voted on) say 'Aye'" clearly refers to something obvious by context. DCDuringTALK 22:21, 3 January 2013 (UTC)
I don't see what sense of favor#Noun (from any favor at OneLook Dictionary Search) that applies.
Also, I have added two senses. Should they be included in or omitted from this RfD? DCDuringTALK 22:31, 3 January 2013 (UTC)
Keep as an idiomatic preposition. A partial synonym is for. As a variant "in your favor", etc. doesn't have "of" but it's still part of the word, similar to "for the sake of", "on behalf of", which become "for your sake", "on your behalf", etc. --Anatoli(обсудить/вклад) 23:06, 3 January 2013 (UTC)
What's that got to do with the price of eggs? Did I ever tell you I hate it when people like you bring up ridiculous example in defense of the outmoted policy that's SOP. Strong KeepPurplebackpack89(Notes Taken)(Locker) 16:07, 21 February 2013 (UTC)
DCD's comment was relevant. Someone proposed "it's a common phrase" as a reason to keep, and he pointed out that it's a fallacious reason, since "red car" is also a common phrase. Equinox◑ 17:19, 21 February 2013 (UTC)
Purplebackpack89, I thought you were a fan of including SoP things, so you think red car is ridiculous but also that we should include it, right? Mglovesfun (talk) 17:23, 21 February 2013 (UTC)
in favor only bears on one of the three senses for which the of is optional. And, even for that one, in favor is an ellipsis that requires that there be something explicit in prior discussion to be in favor of.