use HTML::TokeParser::Simple;

my $p = HTML::TokeParser::Simple->new( "foo.html" )
   or die "can't open foo.html: $!\n";
while( my $t = $p->get_token ) {
   if( $t->is_start_tag('font') ) {
       my $attr = $t->return_attr;
       delete $attr->{face};
       my $attributes =  join( " ", map { qq{$_="$attr->{$_}"} } keys %$attr );
       print "<font $attributes>";
   } else {
       print $t->as_is;
   }
}