Https Cart update quantity Firefox error

I have a website running on Opencart 1.5.4.1. with a Comodo SSL Certificate

When i'm on the cart page and i want to change the product quantity i get the following error
You then have to choose continue or cancel.
I checked the page on http://www.whynopadlock.com/check.php and there it says that everything is secure.
I also get the secure padlock on Firefox so it should work

When i check the page with the firefox Element inspector i see the following error
This error links to jquery.min.js and is a jquery version v.1.7.1
i searched for this error and i read to i need to update to a new jquery.

so my questions.

1. Is the popup error related to the jqeury warning?
2. How can i find out what the problem is because i only get the error when i update the quantity?

Why don't you just upgrade your jquery library?

I was afraid there would be compatibility problems. But it should be no issue?

I tried updating de jqeury by changing the header.tpl from to but that messed up the checkout progress. (the steps didn't fold out).

Could the firefox error come from something different?

From the little research I've done, the JS function in question looks to be related to auto-printing (or equally possibly a html to pdf conversion / pdf invoice). If you have such an extension installed, I would maybe look at disabling it and seeing it the problem goes away.

thanks for the reply and thinking this through. I use a module called PDF Invoice Pro and i disabled it but i still get the error when i change the quantity on firefox.

IE, Chrome and Safari don't have this problem