Ask HN: Why are Google Chrome extensions not compatible with Firefox?

I see many HNers supporting Firefox and lament as it's usage lessens. I do too. Firefox is where I started web development back since the Firebug days.

Today, I was thinking, that if Chrome extensions were compatible with Firefox, won't it's adoption be more?

Couldn't Firefox put some kind of a compatibility layer for a majority, if not all, for the extensions?

After all, they are primarily html, css and javascript, as far as I'm aware.

I guess this is a very simplistic viewpoint as I'm not aware of all the complications that it involves.

Maybe others more knowledgeable can shed some light?