Firefox is increasingly unfriendly to power users. Wouldn't surprise me if they got rid of this feature someday because they have statistics showing few people use it.
I see this so much so, it's to the point that If I see you're using something else, I assume you're not a developer, and you're likely not a power user.
Everyone is there for a different minority used feature. By caring only about the feature used by the majority, you are actually satisfying no one.
That’s why product managers use persona on top of metrics. Nice products have niche features and some kind of personality. You don’t want to overfocus on them but stripping them all is a losing move.
WordPerfect and Quattro Pro (now WordPerfect Suite, I think) seem to persist due catering to special needs of law firms. Catering to some niche users can keep you afloat despite an otherwise market-dominant competitor.
Firefox would have no users at all if Mozilla abandon us nerds and power users who all rely a slightly different set of Firefox's obscure features. If Mozilla were smart, they would embrace us instead of wishing we were more like normal users (if we were, we'd be using chrome already!)
If you only focus on the most popular features you eventually narrow your product to one feature, so obviously there is a balance in there somewhere between focus and utility as well. Identifying why people use your product is as important as knowing what they use. Chrome does all the things I actually use from Firefox, but I use Firefox because when I ever need slightly more hackability it is there for me. That is at best, a once a year occurance.
"WTF" is there to maintain in the feature anyways? If it's such a bloated mess that this kind of small feature causes maintenance issues and a lot of effort to include in subsequent releases, then maybe it is time for Firefox to fail.
Sigh, I've been using Firefox for almost 2 decades, and this is the first I've heard of this feature.