The support article at https://support.mozilla.org/en-US/kb/compacting-folders#w_how-can-i-configure-compact gives the answer to this question as ≡ > Preferences (formerly Options) > Network & Disk Space > Disk Space . However, in ver. 102.15.1, I cannot find Preferences or Options anywhere.. Where do I go? I want to configure compact because, ever since I said to compact automatically some months ago, the compact process causes (1) all emails in the current folder to disappear for some seconds and (2) cancels the conversation thread mode and I have to remember to un-cancel it. If I can work out how to configure compact, I'll probably go back to doing it manually (at times that suit me) to avoid these 2 problems.