the account windows remains as shown and blocks the installation button. only workaround is to navigate with the TAB key to the installation button.
OS is WIN 7 64 bit, IE 11.0.9600.17280
I am having this same issue, however I cannot even use Tab to get behind the account window. Did you ever find a fix for this?
This is still happning my end with SU PRO 64bit 15.2.685, did not find a fix for it. Perhaps something to do with the IE settings - suppose that the Extension Warehous pop up is based on IE. Could be something to with the SSL connection and display of mixed content from the Extention Warehouse - seems that the site is not delivering all content via SSL but some unencrypted. Even in the IE window some drop down remains static…
I was having the same issues using firefox, I switched my browser to chrome and all of the issues went away; draw your own conclusions. I have no idea if this will work for everyone, but it did for me.
Good luck and enjoy