New message editor sometimes deletes letters with acute accents on Firefox

[felipecalvo]

When an acute letter (áéíóú) is inserted and then, very quickly, a space is inserted, the acute letter disappears.

This started happening after the spellchecker was added (https://github.com/mumuki/mumuki-laboratory/pull/1664). I don't think anything else might be causing it and I couldn't reproduce it on Chrome.

As I found this by typing very fast, I believe most users will not notice. Still, the bug is there.