forkuþr : forsiáll (dubious - forsihl inscribed) - no other evidence.
Inscriptional evidence:
foldarr
Add the pre-reformation sources:
foldheiþr (woman foldheid in Agdir 1403, folldeid Hardnger 1439)
Runic:
fróþmarr (fruþmar)
But _post-reformation_:
fróþarr (1740-50 froder Ringarike, froer Vestfold and Sandshverve)
I'll make an exception here, as this post-reformation name has more
than one source _and_ I find it hard to imagine that any such ON
name as *fróþarr could have been invented after the reformation ;)
Runic:
froþolfr (runic fraþulf) : fraþi & fraþa (2 cases of the short form
for masc. names in fraþ-)
Saga-literature:
fraþmarr (alternative to fróþmarr perhaps, but a parallel stem of
the same meaning, compare Gothic fraþ-)
Runic none, saga-literature 2:
fiorleifr : fiorleif - no other sources
Runic:
fiolvarr (fiuluar, fiuluars) : fiolmóþr (fiulmuþ)
Saga-literature:
fiolviþr : fiolmundr (both about the same person) - dubious
As far as I know, there are no other ON compound names beginning on
the letter f in ON, besides fránmarr, fríund and possibly fiolnir,
if we are to interpret that as a man's name in some cases. fróþi is
also short for names in fróþ- (2 above, compare fraþi).