Using arrow keys to deselect text after applying style fails in Firefox

[peterchappell]

Description

In Firefox, if you select some text, apply a style via the toolbar and then use the left or right arrow key to de-select the text, nothing happens.

Steps to reproduce

1. Use Firefox
2. In an editor, select some text
3. Apply style/formatting via the toolbar
4. After the style has been applied, use an arrow key to de-select the text

(Compare against other browsers)

Expected behavior:

The text should be deselected and the cursor should be positioned accordingly (e.g. after applying a style and then clicking the "right" arrow the cursor should be to the right of what was previously selected.

Actual behavior:

Nothing happens.

Link to an example:

This can be reproduced on the demo page (using Firefox)

Versions

• medium-editor: 5.23.3
• browser: Firefox 65.0.1 (64-bit)
• OS: MacOS (Mojave)