I recently switched to Firefox, for a number of reasons that really aren't relevant to this post, but his arguments (at least in the summary) don't hold water in my experience.
(1) Pocket: One of the first things I remove when customizing FF. I've not seen anyone suggest it, and seen a fair amount of dislike for it.
(2) Memory Use: Perhaps valid prior to 2000, but c'mon, every system I've worked with (both at home and at work) have a minimum of 16GB of RAM, the days of a 4GB system with a spinner drive are long long gone. Pop on some, quite required actually, ad-blockers, and use isn't any worse than Chromium or Safari browsers.
(3) Failing to load websites: Name one. In point of fact, since Chrome and Edge are built under the same structure, I often use FF to troubleshoot website weirdness to see where the problem really is. Sure, experience of one here, but I've not seen any site (from private, individual user, to public corp to gov't) mis-load under FF.
(4) Personal data for sale: Okay, I'll give him that, if he can prove it's happening.
(5) Low browser marketshare: So? Does FF stop working because it's got a small number? Quick, better let Linux know this!
This guy sounds like he's whinging just to put out some clickbait article. Not buying it.