I've been using Thunderbird for a long time but this is something I've not seen before today. I was editing an old message (via 'Forward') to produce a new message - an agenda for a regular meeting. I started to delete words from a line of text, going from the right-hand side using the backspace key. When I reached the beginning of the first deleted word (i.e. after deleting the first character in the word, before I could delete the preceding space) the cursor jumped about 20 characters to the right, as if a big tab had been inserted. The line now had extra space characters on the end of it. I could delete those with Backspace one at a time and then move on to the next word now at the end of the line. When I reached the beginning of that word the cursor jumped to the right again - though not necessarily by the same number of characters. Weirdly, this didn't happen with every word. Sometimes I could get to the beginning of a word and could go straight on to delete the space in front of it. Deleting text by other methods (e.g. using the Delete key to go from left to right, or highlighting text and using Ctrl/X) work as normal. This is not a phenomenon limited to a specific message. I've tried editing other messages and the same thing happens, but with different numbers of spaces inserted. I'm really not sure what's going on or why it has suddenly started to happen. Can this issue be replicated by others? I'm currently using Thunderbird 140.0.1 on up-to-date Windows 11 (though I was using 139.xx earlier today when I first noticed this).