Firefox @page{margin} issue

Page has a rule that overrides user-set margins:

@media print {
  @page {
    margin-top: 0.2in;
    margin-bottom: 0.2in;
    margin-left: 0.2in;
    margin-right: 0.2in;
  }
}

This script can override the tiny margins specified in @page, but it would be better to just disregard those margins if they are smaller than what the user specified:

// Override @page{margin} rule if found
var docSS = document.styleSheets, ss, ess; 
for (var i=0; i<docSS.length; i++){
  if (!docSS[i].disabled){
    // check content of style sheet for @page (type 6 style sheet)
    // https://developer.mozilla.org/docs/Web/API/CSSRule#Type_constants
    ss = docSS[i];
    for (var j=0; j<ss.cssRules.length; j++){
      if (ss.cssRules[j].type == 6){ // Page sheet
        if (ss.cssRules[j].cssText.indexOf('margin') > -1){
          // Try overriding to 0.5in top/bottom, 0.25in left/right
          ss.cssRules[j].style.margin = '1.27cm 0.64cm';
        }
      } else if (ss.cssRules[j].type == 4){ // Print Media sheet
        // Check for any embedded Page sheet inside
        ess = ss.cssRules[j];
        for (var k=0; k<ess.cssRules.length; k++){
          if (ess.cssRules[k].type == 6){
            if (ess.cssRules[k].cssText.indexOf('margin') > -1){
              // Try overriding to 0.5in top/bottom, 0.25in left/right
              ess.cssRules[k].style.margin = '1.27cm 0.64cm';
            }
          }
        }
      }
    }
  }
}