Firefox is sitting at 8.3% quota in NA and dwindling. It's reasonable not to support it.
- 8.3% is almost much larger than the metric you actually care about -- the percentage of users that will not use Chrome (or your desired set of supported browsers).
The desired set of supported browsers will always come down to metrics.
Essentially, both companies have done anti-privacy and untrustworthy actions, and choosing the lesser evil is hardly ideal.
The 8,3% (or 9,52%, or whatever) of Firefox users is way, way beyond total Skype users. Firefox has about ~170M users, Skype 4,5M.