A Blog From Behind the Trenches

If you go to fitness-superstore.co.uk and click the image abov "Click image to enlarge", a popup is supposed to open. This does not happen in Opera, but it works fine in IE and Firefox.

But why?

If you open Opera's error console, you will notice the following error in the site's script:

name: ReferenceError
message: Statement on line 60: Undefined variable: imgWin

If we go back to find out how "imgWin" is set, we find this:

if (isNN){imgWin=window.open('about:blank','',optNN);}
if (isIE){imgWin=window.open('about:blank','',optIE);}

So we have isNN and isIE, which refer to Netscape Navigator and Internet Explorer respectively:

var isNN=(navigator.appName=="Netscape")?1:0;
var isIE=(navigator.appName.indexOf("Microsoft")!=-1)?1:0;}

The site clearly assumes that IE and Netscape are the only browsers in the world. But it still works in Firefox, so what's going on?

It looks like Firefox's roots are still visible in navigator.appName: Paste "javascript:alert(navigator.appName);" into Firefox's address bar, and the JavaScript alert dialog will return "Netscape". Opera, on the other hand, reports itself as "Opera", and this tiny detail breaks the popup script.

One could say that Firefox is a "new version of Netscape". It comes from Netscape's code base, and initially used the "Netscape engine" (Gecko). Even before Firefox existed, many sites were updated to work with Netscape 6 because most Web developers knew about Netscape. Even today, it looks like most Web developers take Netscape into account when working on their sites.

So when Firefox was created it, in a way, got a "free ride" because of its Netscape roots and because it used the "Netscape engine".

I am not sure when we decided to return "Opera" for navigator.appName, but there has been discussion at Mozilla to do the same with Firefox. Considering Asa's cheering when we stopped spoofing as IE by default it is rather puzzling that they have not gotten around to accurately representing themselves yet

In any case, I hope this can be useful to at least understand a small part of the compatibility issues alternative browsers face today: The quite common assumption that there are only two browsers out there.