Read again. I quoted something along the lines of "just as much a development decision as a marketing one" and I said, it wasn't a development decision, so what's left?

Firefox released just as frequently before, just that they didn’t increase the major version that often.

This does not appear to be true.

Why don't you take a look at the version history instead of some marketing blog post? https://www.mozilla.org/en-US/firefox/releases/

Version 2 had 20 releases within 730 days, averaging one release every 36.5 days.

Version 3 had 19 releases within 622 days, averaging 32.7 days per release.

But these releases were unscheduled, so they were released when they were done. Now they are on a fixed 90-day schedule, no matter if anything worthwhile was complete or not, plus hotfix releases whenever they are necessary.

That's not faster, but instead scheduled, and also they are incrementing the major version even if no major change was included. That's what the blog post was alluding to.

In the before times, a major version number increase indicated major changes. Now it doesn't anymore, which means sysadmins still need to consider each release a major release, even if it doesn't contain major changes because it might contain them and the version name doesn't say anything about whether it does or not.

It's nothing but a marketing change, moving from "version numbering means something" to "big number go up".