Changing behaviour of Account Creation and Checkout

[wol4]

I have Prestashop (1.6) running in an iFrame that cannot change it's height after loading.

 

That works fine, except:

 

Checkout and Account Creation pages sometimes change their height without loading the whole page again.

Can't see the bottom of the page (address and changes in shipping or payment) and can't scroll down!

 

For my case, I need to change that behaviour (or change to another iFrame script)!

 

➡ How (and where) can I tell Prestashop to always load the whole page for account creation and chekout pages?

 

Probably I will have to use the "steps" checkout.

Edited September 17, 2016 by wol4 (see edit history)