Problem with commenting in popup

Clicking ‘Comment’ button below any answer shows a popup for comment, while everything in background becomes shaded and non-scrollable — this is a problem (especially on small mobile screens), because a user may need to scroll back for reminding or quoting something from the conversation.
I suggest to make an option to load an inline comment form right instead of the ‘Comment’ button when it’s clicked, or show a floating comment form attached to the bottom of the screen, while keeping page content scrollable.