IIRC the Core is using v1.1.10 whilst this extension is just a minor version "behind". Judging from a comment in the latest 'appbrowser.cxx' I have the impression that Robert is already using v1.1.10.
Not being really a FLTK user I wonder whether some more related extensions could do with an update (e.g. 'libfltk-xft.tcz').