The difference is that Verizon-Checkmark is clearly an invalid interpretation - the checkmark is obviously decorative.
Mozilla's new logo was chosen specifically due to the double meaning, the similarity between the symbols :// and the glyphs "ill".
The ambiguity is what makes it "clever", and it's kind of an in-joke that most non-tech people, who've never heard of "Mozilla" as such, won't immediately register. They'll read the characters literally and say "moz://a? Is that a new computer thing?"
I don't think that's an idiotic response at all.
This is a bad generic logo merely because it doesn't clearly communicate their company's identity in a unique and obvious way, which is the sole function of a logo in the first place. I could see this rendering appearing at some hacker events or on t-shirts, but IMO it makes no sense to use it as a generic logo.
I don't even want to think about the nightmare of accidentally rendering the string "moz://a" in a typeface that the lawyers consider too similar to that used in the logo.