($ENV{HTTP_USER_AGENT} =~ /MSIE/)
&& do {
  # Internet Explorer
  $style{'body','font-size'}='10pt';
  $style{'th','font-size'}='8pt';
  $style{'td','font-size'}='6pt';
  $style{'pre','font-size'}='10pt';
  $titlebox_size='4';
  1;
} || do {
  # Netscape
  $style{'body','font-size'}='10pt';
  $style{'th','font-size'}='10pt';
  $style{'td','font-size'}='8pt';
  $style{'pre','font-size'}='10pt';
  $titlebox_size='5';
};
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On an unrelated basis to your actual problem, I do like to use short circuiting logical operators for flow control. But then the rule of a thumb is to use low precedence ones for this, and high precedence ones to operate on values (of course it actually doesn't make a difference here). However in this particular case they won't buy you anything over a regular, proper, if... else. Just so to let you know. Incidentally if you do so you won't incur in the "misplaced" warning line you're incurring into now.