I don't believe so, but we target everything in the Webkit ecosystem (Chrome, Edge, Safari), so Firefox would be the only odd browser out.
From a user perspective, we used to get asked all the time to support Firefox for Streak. Those requests have mostly disappeared more recently - seems like our user base is predominantly Chrome and Edge.
Could it be because Firefox users have given up? I wonder what percentage of your user base would be Firefox users if it were supported. Of course I don't have an answer to that, but I don't think lack of requests necessarily translates to lack of interest.