Either windows’ or windows’s is correct, actually. The reason is because of exactly words like “Windows”, if you use the former, it sounds like it’s a possessive of more than one window, but it’s a possessive of a proper noun, Windows. The latter is more correct in this case because of that. (it’s also pronounced that way!)
Something that annoys me about people who love to harp on about how bad Mozilla is because they’ve gone downhill (which they have): Who is better? Genuinely compare them to their competition. Google? Heck no. Brave? Nope. Microsoft? Absolutely not. Apple? No. People complain about how much Mozilla spends on advocacy, but then when they actually do the advocacy, they’re happy about it! They’re perpetually stuck between a rock and a hard place because they’re pulled in both directions and thus, Firefox suffers. But, are they actually a broken clock? Really?
I guess to be a little clearer: If you compare Mozilla to their past selves, they lose. If you compare Mozilla to anyone else in that space with the resources to develop a browser, they’re still the best of the bunch by a country mile.