Green’s Dictionary of Slang

muffer n.

[muff v.2 ]

1. (US) a lesbian; i.e. a woman who performs cunnilingus.

E. Hoagland Circle Home 191: I’m going to sleep you in with Maud. She has this streak of muffer in her and I’m trying to broaden her out [HDAS].
[US]B. Rodgers Queens’ Vernacular.

2. see muff n.2