Detect Permission Error Before Die

I'm trying to pass information to a popup window without using the URL query string. I'm accessing the variables directly from the parent window, like:

Code:
window.opener.myVar

...and after the first load, I'm saving them into a cookie in case the parent URL changes and the info is no longer available. Problem is, in Firefox, I'm getting a Permission Denied error if the parent window has moved on to another URL, and JavaScript stops before then trying to get the information from the cookie.

Is there a way to detect if the page has permission to access the variable without killing scripting? I've tried things like...

if (window.opener.myVar) { }
// ...and...
if (typeof window.opener.myVar == 'object') { }
...but just attempting to access the variable kills JavaScript in Firefox.

I suppose I could check if the cookie exists (it's written when the page loads the first time), and if so, not even try to access the opener variable, but I thought I'd check for a more elegant approach.