Visual Chars plugin randomly inserts ` ` in Firefox

1. Go to https://www.tiny.cloud/docs/tinymce/latest/full-featured-open-source-demo/
2. Mark all the text and delete it
3. Type in some random text with spaces and check the source. The text is exactly as you typed it
4. Go to "View" and check "Show invisible characters"
5. Enter another text with spaces. Absolutely random   appear after you've pressed the space bar.

This error only occurs in Firefox (tested in v139), and neither in Chrome nor Edge.