There is an unwanted scroll to top effect inside Page Builder when a block is dragged from the sidebar to the page.
Steps to reproduce
1. Edit page in Page Builder. Be sure that page that you are editing is higher than working window.
2. Scroll to the bottom of the page.
3. Start dragging one of the blocks into the workspace.
The page will be scrolled to the top.
this unwanted effect affects only Firefox Browser on Windows 10 and iOS (on Ubuntu it is fine). Tested on Firefox 61.0.1, 61.0.2.