> It does make development easier, and at some point it just doesn't make sense to support any longer.
It depends on what you're doing. If you're building an app (something which would make more sense as a native program anyway), then sure — use JavaScript. But if you're displaying text and images, then HTML & CSS are perfectly capable of handling that.
In general, I think that a good content-focused website will work equally well across all browsers. There's no need to force end-users to allow you to execute code on their machines in order to display paragraphs or images.
> I'm more worried about the recent trend of sites not even working in Firefox anymore, just Chrome.
And I'm worried about the long-standing trend of sites not even working in lynx, links, elinks, eww or w3m anymore, just Firefox, Chrome & IE.