I suggest Mozilla look at the last 6 months of bugs submitted and do some analysis on them.
Ideally take a subsample and talk to the submitters, and see what they think.
If Mozilla agree that Google do a better job than Mozilla, then benchmark against them.
I eventually stopped reporting bugs to Mozilla, Microsoft and Apple unless I absolutely had to. I recently stopped working with browsers, so I no longer have much appetite for helping.
Maybe someone from Mozilla's community outreach can comment and ultimately make some improvements.
Specific examples of said bug reports would probably help, though.