This is an anti-feature. Firefox enabled a deprecated standard because Google couldn't be bothered to move to the current standard. Classic catering to the big players.
They held off for a very long time, and I'm glad they did that. I'm also glad they switched, because the alternative is that either you don't use the most effective security option available or you stop using Firefox, both of which seem like even bigger long-term problems.
The goal of a web browser is to browse the web, not to browse most of the web. Principled objection to a site doing something nonstandard is great when the goal is to get the site to fix it, so the browser's users can visit that site. Once it became clear Google wasn't going to fix it, refusing to ship support (that was already implemented!) only has the effect of hurting Firefox's users (slash telling some fraction of Firefox users to stop being Firefox users anymore) and not improving the web or maintaining internal engineering standards.
