(Please scratch the bottom of the page part, it doesn't work anywhere).

I tried reproducing this on http://it.wikipedia.org/wiki/San_Francisco in both Firefox and Chrome, but both editing existing links and adding new links works for me.

I can confirm this bug on en.wp, but not on nn.wp or mediawiki.org

Roan: right now in that page, if I click on "California", I get a "page found" text and two arrows which allow me to scroll a list of alternatives (which do not look handy since they only allow to preview one line at a time).
A few lines below, if I click on "architettura moderna", I don't get alternatives.
If I write somewhere, say, "USA" and try to make it a link, that will work, but I still don't get to decide which page the link should point at.
In FF, it doesn't work with Vector. It's both browser and skin specific, for me.

Yup, I can reproduce this now. It looks like in some cases, the selection dropdown isn't shown properly, it retains display:none; and height:0; (but the suggestions are there, I can see them in the DOM inspector). I think this may have to do with the unreliable behavior of nested .show() calls in jQuery in Firefox: I've observed that sometimes, calling .show() on a container doesn't immediately cause its children to evaluate as visible, which means that calling .show() on those children is a no-op because .show() refuses to touch things whose parent is hidden. The height:0 is likely due to trying to measure a hidden element.

CC Trevor.

I believe that this is now fixed, at least as far as I can tell.