Last typed-in number or character not shown unless another keystroke

I sometimes notice that after typing in a number or character in a website form field in Firefox that the character or number isn’t immediately displayed. It takes another keystroke for that. Clicking the cursor somehere in side a word behaves similarly sometimes. I think it sometimes happens in other software like iotas or Apostrophe as well, but I’m not quite sure.

If you need more info, I’ll gladly provide it.