Chrome's font rendering is the outlier among browsers. The author of the article is seeing that difference and they want Firefox to look like Chrome.
I think the commentary is taking an issue with the suggestion that there's something "wrong" with Firefox's font rendering, when it's really Chrome who is the outlier.
Maybe we need a screenshot from Safari to compare and break the tie.
As of right now there's substantially more browsers that use Blink (and comprise over half of the market share) though so Firefox and Safari will always be outliers.
On macOS, it looks like Firefox uses native defaults. It’s very nearly identical to Chrome (same fonts, same weight, same spacing; Chrome might more aggressively aligning verticals to pixel boundaries, but that’s hard to tell on a Retina screen).
Safari for some reason is rendering everything at different sizes than Chrome or Firefox, I don’t know why.
I think the commentary is taking an issue with the suggestion that there's something "wrong" with Firefox's font rendering, when it's really Chrome who is the outlier.