The older version didn’t have this issue, my best guess is the number of form elements is making the browser lock up and the older version had more efficient form element alteration. It’s very bad for me because I develop for woocommerce so I have to enable the extension to login and then disable it to get work done 
What’s Woocommerce and how would one reproduce this problem you mention?
Hello! Woocommerce is an ecommerce system that is one of the best out there atm in my view at least, even though it is built on top of Wordpress. Basically when I go to the products page firefox tells me that an extension is causing slow downs and the browser locks up the extension it names is Kee. When I disable it the issues go away. The way to replicate this is probably hard if you don’t have a woocommerce with enough products in it. I could probably save the html page and send it to you somehow for you to test though. Or you could just create a page with a lot of input elements and see how performance really dips. As the page is going to have a lot of sensitive product info on it I can email you a zip of the page in question if that’s easiest. I checked and saving the output to html does replicate the issue.