Technically it wasn't a tab, that was just the 'UI' that was used on
those three pages. We currently, as far as I can tell, no longer have a
page to point to for people who want to contribute in some way; there
are only the 'sponsor' and 'donate' pages, which isn't all types of
contribution mentioned on the old page.
I have been pointing to it from the Jaybird release notes for the past
few years, and now it gets you nowhere near its intended goal. Can it be
reinstated in some way, and otherwise be made to redirect to
http://www.firebirdsql.org/en/community/ as that seems to be a better
page than the main page for this goal.