Please do not take this in any way as a judgment of Firefly, but to the eyes of corporate suits it has to just look like off-brand Star Wars (and honestly, I love it, but it really is in most ways that matter). I don't see how Disney ends up making it.
They own the leading brand franchise, so I don't see how major investment in the off-brand make sense to media conglomerate brains. If Star Wars shows are doing well and they receive a Firefly pitch then it will probably become a Star Wars show about a crew of lovable misfits trucking around between planets on a funky and cobbled together but somehow exceptionally high performance ship, on the run from authorities and having various episodic Sci-Fi adventures. A lot of Star Wars is like that, and that is where Joss Whedon got the damned idea in the first place. He developed it more than any Star Wars media ever did, and is a strong writer in a way George Lucas certainly never was with a level of authorial control that most the non-Lucases helming Star Wars media have not had, but core concept-wise Firefly is the "Millennium Falcon in the old west" and for those not invested in the Firefly universe's lore the same stories mostly fit the galaxy far far away.
If Star Wars shows do poorly and they get a Firefly pitch then Disney executives will just assume that audiences have lost interest in all things Star Wars like and not make it for that reason. because that is how megacorporate media conglomerate brains think.