editableText.EditableText._hasCaretMoved: only fall back to checking if the word at the caret has changed once _hasCaretMoved_minWordTimeoutMs has elapsed. I.e. 30 ms must elapse before starting to check the word.
This fixes a regression introduced by #7201 where deleting characters in Mozilla Gecko editable controls would cause the character being deleted to be spoken rather than the character that followed.