'unsupported browsers' are browsers that are old or broken. FireFox is a perfectly good browser, it is current and should be supported.
'supported browsers' are browsers that you lose customers if you don't support. You don't lose customers by telling them to switch to Chrome. Firefox's market share is small and the number of people who exclusively use Firefox and refuse to switch is vanishingly small.
That's a great attitude towards your users. No, you, the vendor, adapt to what your users bring.
That is the standard that the web was built around. Lazy developers that only wish to cater to the one browser that they have on their desk and that refuse to recognize that the world is a bit larger than their minimal view (including screenreaders and other accessibility device) should get another job. And if the company they work at is run competently they will (Microsoft apparently is not one of those, but that's not really news either).
If a browser is standards compliant it should be supported. Note that standards are there for a reason, they create a level playing field. So all you really need to do is to ensure that your implementation is conform the standard, you then still have to test to ensure that your assumptions hold in light of practical applications of that standard on the rendering side. But there really is absolutely no excuse why barring non-standard extensions your website would not work with all browsers with more than 1% market share.
https://en.wikipedia.org/wiki/Usage_share_of_web_browsers
Would be a good place to start for your compatibility testing.
- 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.
Yes, you do. It might be a very, very small number, so small that you decide not to care about it, but you definitely lose people.
The tricky part is that most companies have no idea how many people they lose and why. It's just marketeers guessing and anecdotal evidence. The number is probably bigger than they think, because generally speaking, marketeers are not the type of persons that about browsers.