Sidebar Resizing Inconsistent

Hi, I have been experiencing this issue on a Surface Pro 3 ever since version 5. If I drag the entire extension window, then resize the left sidebar, it will incorrectly resize. If I open the extension, then resize the sidebar WITHOUT moving the window, it will work completely fine.

This occurs on the latest version of Firefox & Kantu as of 09/03/2019, running on Windows 10 on a Surface Pro 3.

(Only happens on the Surface Pro 3. Tested on 3 different computers without this issue)

Can you please add a screencast of how this looks?