This is an OLD problem through SEVERAL versions of Thunderbird and I’ve tried searching at Mozilla and can’t find anything. Maybe my search term is awry!
Every once in awhile when I’m composing a new email message of multiple paragraphs, I get to the end of a sentence and enter a period (stop). When I start to type the next sentence, Thunderbird inserts a “carriage return” and starts my new sentence there. I have to go back up to where my sentence ended and hit DELETE to get the new sentence in its proper place.
Has anyone run into this and possibly know what’s wrong – a stray setting on my part or a (shudder) long-time software bug?