What is the copyright of a patch waiting for approval?

Here's the scenario:

Person 'A' submits a patch to bugzilla.mozilla.org. It's waiting to be
approved. Person 'B' comes along and see a snippet of code that would
be great for his patch to submit to mozilla. Is this allowed?

What is the copyright of the patch?

A slightly different scenario would be a patch that is not accepted
but someone else wants to take it and rework it.

I don't see any blurbs at developer.mozilla.org about whether or not
copyright is assigned, either at the time of submitting or after.