I too could be misunderstanding this, but Firefox does not display extensions within itself.
It merely takes you to the main page that does.
So I am guessing that yvan would like that foobar would have the link for the main component/plugin page built right into it.
As Lyx stated, neither one has a single page that contains all the plugins/components/etc...
Although, I will give Firefox the credit that the process of installing an extension is contained within the UI (you click on the link and then y ou click on a dialogue whether you wish to install it or not). there's no need to uncompress the file into a directory as in the case of foobar. -my argument for foobar is that MOST technically challenged people don't bother with foobar and thus most users of foobar are capable of installing its components.
-PS: I actually give Firefox a LOT of credit. I love this browser and it's the only one I use except in the case of needing to use windows update where one is forced to use IE.
of course, this is way OFF topic.