This is wrong. And by mixing up the L and R, it is wrong in a way that boomerangs nicely on people who poke fun at Japanese speaking English. [Not that I think that's what Currie, of all people, was doing.]
Mujirer is a transliteration of Mujiraa [ムジラー], which is, in fact, what some people call Muji addicts. [As a 10-year-plus Muji obsessive, I confess I've never heard or read this term, but it's out there, so I'll go with it.]
The Japanese syllable ラ, is the one that's used to transliterate both L and R. Sonically, it's somewhere in between. Where Mujiraa is easy and smooth to say in Japanese, in English, Mujirer sucks. Before this Mujirer thing gets too far, I suggest using comparable Japanese words to come up with a better Roman spelling:
One possibly etymology for Mujiraa [ムジラー} is Gojira [ゴジラ], the Japanese name for Godzilla. Compare that to Mozilla, which is transliterated as mojira [モジラ], and except for the long A at the end of Mujiraa, you could make the case for Mujilla.
But I think there's a better option. The Japanese transliteration of killer--and killah, for that matter, as in Ghostface--is kiraa [キラー]. This pattern would transliterate Mujiraa as either Mujiller or Mujillah. Either one of those is more accurate and sounds better than Mujirer. Use the former for Muji nerds, and the latter for badass Mujihadin who are smuggling suitcases full of that no-label stuff back from the mothership in Yurakucho on a regular basis.