This has been happening for a long long time - probably a few years' worth of versions. I have just put up with it... currently running Tbird 147 and it just happened. When editing an email (either the body or the Subject), if you use the backspace button (the one that deletes to the left) to delete some text sometimes the cursor will incorrectly be positioned about 5 or 6 characters further left than it should. For example, if I had the text: "Quick brown fox jumps over the moon" If I were to highlight "fox" in the above example, and hit backspace, I would expect the cursor to end up positioned between the remaining spaces after 'brown' ( pipe symbol here is meant to represent the cursor position): "brown | jumps" But instead what happens is that the cursor ends up somewhere among/before the word "brown". It's always further left than it should be, by 5 or 6 characters. I believe it only happens when highlighting multiple characters and then hitting backspace. It may be more (only?) prevalent when editing/replying to an existing email. (But I'm still only editing the new portions that I add at the top of the email; I'm almost never editing in amongst the original quoted email content.) I also haven't ever been able to figure out how to make it happen, sorry. It is just random...It will happen once in an email, but then not again. But it happens frequently - 3-6 times a day perhaps. (Depends on how many emails I am editing. :) ) I don't believe that I have noticed this issue if I were using the Delete button (deletes things to the right). I don't think it happens when backspacing one character at a time...but it might. I also use Option-Backspace to delete whole words at a time (instead of highlighting the word); not exactly sure if it happens only if highlighting a word, or only if Option-Backspace, or single key press... sorry, it is so random and unexpected that I don't have more specifics.