If it's a CGI program, the program doesn't "work" in Firefox nor in IE. Or any other browser for that matter. CGI is a protocol that is talked between an HTTP server and a back-end program (the browser being a front-end). Such back-end programs are called 'CGI programs', and they never talk to browser, and certainly don't work in browsers.

Without knowing more of the code, it's hard to tell what print $val, br; is supposed to do. If there's a br subroutine, the code will print the value of $val, followed by the return value of br in list context - and unless its return value is ", br" (sans quotes), that will be different from print "$val, br", which will print the value of $val, followed by a comma, a space, the letter b and the letter r.

However, if br isn't a subroutine, the code shouldn't compile under strict, and generate a warning under warnings.