Describe the bug

When adding new blocks in Firefox 71 they appear overlapping existings blocks. This behaviour was not encountered in Safari when tested on MacOS Catalina.

The blocks don't push the next block out of the way and appear on top of eachother. I've replicated this using private blocks in a client project, and in frontenberg with the latest gutenberg

Of note this doesn't happen with paragraph blocks and bullet lists, but does happen with columns, and sometimes it jumps to the correct layout

To reproduce
Steps to reproduce the behavior:

1. Add a block or blocks
2. Observe overlapping

Expected behavior
I expect behaviour to match behaviour in Safari as is normal for block insertion

Screenshots

https://youtu.be/6RQpVWZvFc0

Desktop (please complete the following information):

• OS: MacOS Catalina
• Browser Firefox
• Version 71

Additional context

• Gutenberg 7.1, and stock WP 5.3