Is that a good thing?
I'll take Mozilla over Google every day, but if Mozilla presents itself as open to community, it also lends itself to criticism that Google avoids altogether.
So yes, that happens, and if that's not as easy as we could have hoped, probably help is welcome with that as well.
Big and complex projects generally have higher standard of effort necessary to get the leg in. The comparison to Chrome was that it's a project comparable in complexity, and yet Firefox is easier and faster to build.
I've submitted many browser bug reports to Google, Microsoft, Apple and Mozilla over many years. I only bother to submit issues for "important" bugs, I write clearly, I simplify, and I spend significant time ensuring that the bug report is useful to developers and relevant for users.
Google respects my efforts, and often fixes my reported issues, or at least explains why it can't be fixed (usually with well reasoned answers, usually the actual developer is communicating with me).
Microsoft/Apple/Mozilla waste my time, ignore my efforts, and generally that results in a poorer user experience in the browser.
The Chrome team is one of the most amazing software teams I have ever been tangentially involved with - and the product quality shines.
Maybe someone from Mozilla's community outreach can comment and ultimately make some improvements.
Specific examples of said bug reports would probably help, though.
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.
I have no trouble believing that contributing to Chrome is even harder, but then again I didn't hear someone from Google saying "If you think a bug is easy to fix, pleasez consider providing a patch."