Currently in Thunderbird Mobile when replying to an email it is a reply by default, while reply-all is hidden behind the three dots ". . ."
Most of the time, in my experience, I have to reply-all, as the cc's are just as important to include. The extra step of clicking the ". . ." can be overlooked in the rush, leading to a communication conundrum.
Let me know what you think and thanks a lot for your great work!