This probably doesn't work ... somewhere? But on the all the most pathological pages I could find (sample of 5 in the DATA section), it seems to do fine.

#! perl -slw
use strict;
use LWP::Simple;

while( <DATA> ) {
    chomp;
    my $html = get $_;

    $html =~ s[( <FONT \s+ (?: (?:"[^"]+") | (?:'[^']+') | [^>]* ) > )
+]  #"
    {
        my $tag = $1;
        $tag =~ s[ face \s* = \s* (?: (?:"[^"]+") | (?:'[^']+') | [^\s
+]+ ) ][]ixm; #"
        $tag
    }eximg;

    my $out = $ENV{TMP} . '\\' .time() . '.htm';
    open OUT, '>', $out or warn $!;
    print OUT $html;
    close OUT;
    system( $out );
}

__DATA__
http://www.webdiner.com/annexe/font/font.htm
http://www.electricearl.com/fonttest.html
http://www.ilovethisplace.com/webdesign/fonts.html
http://www.york.ac.uk/depts/maths/symbchrc.htm
http://www.tedmontgomery.com/tutorial/style.html#face
[download]

Note: system probably won't load the modifed sample directly into the browser on systems who's commands line don't know what do with .htm files.