@Reconstructo,
Any "first science" must provide the grounds for both itself and for the other sciences, even though---when seen from special horizons---each science can be said to provide this ground. Hence we find conflicting claims for priority from anthropology, history, and many other specialised disciplines or ways of knowing; even religion and literature make such claims.
Yet, can any of these justify themselves from
within their ways of understanding? Only by transcending their perspectives or special ways of looking at the world, only by appealing to another source that can establish the validity of their rules and procedures and perspectival processes can they do so, and that over-reaching "science" and source is philosophy, and all those "philosophies
of" their disciplines to which each appeals when in doubt.
And alone of all these human endeavors of knowing (science), it seems that only philosophy can even
begin to provide its
own ground in the discipline of meta-philosophy.