Emulate print media in Firefox 62 (userscript work in progress)

showAsPrint.js

// For Firefox's Web Console, creates the functions showAsPrint() and undoShowAsPrint()
// to roughly emulate print media and revert
function showAsPrint(){
	var docSS = document.styleSheets, ss, oldMedia, newMedia, rules;
	var p2s = function(media){
		if (media.indexOf('all') > -1) return media; //no need to change
		if (media == 'print') return 'all, wasprint'; //show on screen, too
		if (media.indexOf('print') > -1 && media.indexOf('screen') > -1) return media; //no need to change
		if (media == 'screen') return 'wasscreen'; //hide these rules
		if (media.indexOf('screen') > -1) return media.replace('screen', 'wasscreen'); //hide these rules
		if (media.trim().slice(0,1) == '(' && media.trim().slice(-1) == ')') return media; //too hard to parse
		return media + ', WTF'; //for debugging only
	}
	for (var i=0; i<docSS.length; i++) {
		ss = docSS[i];
		if (!ss.disabled){
			if (ss.ownerNode && ss.ownerNode.id.indexOf('stylus-') == -1 && ss.ownerNode.id.indexOf('stylish-') == -1){
				// check link or style tag for media attribute and edit as needed
				if (ss.ownerNode.hasAttribute('media') && ss.ownerNode.getAttribute('media') != 'all'){
					oldMedia = ss.ownerNode.getAttribute('media');
					newMedia = p2s(oldMedia);
					if (newMedia != oldMedia){
						//console.log('Updating: ' + ss.ownerNode.outerHTML + ' to ' + newMedia);
						ss.ownerNode.setAttribute('media', newMedia);
					}
				}
				// check content of style sheet for media rules
				try { 
					rules = ss.cssRules; 
				} catch(err) { 
					console.log('Can\'t access cssRules for ' + ss.href + ' due to: ' + err ); 
					rules = []; 
				}
				for (var j=0; j<rules.length; j++){
					if (rules[j].type == 4){
						oldMedia = rules[j].conditionText;
						newMedia = p2s(oldMedia);
						if (newMedia != oldMedia){
							//console.log('Updating CSSMediaRule from ' + oldMedia + ' to ' + newMedia);
							rules[j].conditionText = newMedia;
						}
					}
				}
			} else if (!ss.ownerNode){
				console.log('No .ownerNode on i=' + i);
			}
		}
	}
}
function undoShowAsPrint(){
	var docSS = document.styleSheets, ss, oldMedia, newMedia, rules;
	var unp2s = function(media){
		if (media == 'all, wasprint' || media == 'all,wasprint') return 'print'; //undo applying to screen
		if (media == 'wasscreen') return 'screen'; //undo hiding
		if (media.indexOf('wasscreen') > -1) return media.replace('wasscreen', 'screen'); //undo hiding
		return media; // otherwise, we didn't mess with it
	}
	for (var i=0; i<docSS.length; i++) {
		ss = docSS[i];
		if (!ss.disabled){
			if (ss.ownerNode && ss.ownerNode.id.indexOf('stylus-') == -1 && ss.ownerNode.id.indexOf('stylish-') == -1){
				// check link or style tag for media attribute and edit as needed
				if (ss.ownerNode.hasAttribute('media') && ss.ownerNode.getAttribute('media') != 'all'){
					oldMedia = ss.ownerNode.getAttribute('media');
					newMedia = unp2s(oldMedia);
					if (newMedia != oldMedia){
						//console.log('Restoring: ' + ss.ownerNode.outerHTML + ' to ' + newMedia);
						ss.ownerNode.setAttribute('media', newMedia);
					}
				} else {
					// check content of style sheet for media rules
					try { 
						rules = ss.cssRules; 
					} catch(err) { 
						console.log('Can\'t access cssRules for ' + ss.href + ' due to: ' + err ); 
						rules = []; 
					}
					for (var j=0; j<rules.length; j++){
						if (rules[j].type == 4){
							oldMedia = rules[j].conditionText;
							newMedia = unp2s(oldMedia);
							if (newMedia != oldMedia){
								//console.log('Restoring CSSMediaRule from ' + oldMedia + ' to ' + newMedia);
								rules[j].conditionText = newMedia;
							}
						}
					}
				}
			} else if (!ss.ownerNode){
				console.log('No .ownerNode on i=' + i);
			}
		}
	}
}