Was just updated to version 115.5.1, and I had held off posting this question until after the update, hoping the issue might be resolved... but it's as bad as ever. Tbird abruptly became very slow to delete/display messages; not with the last update, but a couple of updates previously. I have been in the habit of working my way up the list from the oldest to the newest, and as I hit "delete" and "up arrow" to view the next email, it's a slow, laggy process. Both emails remain highlighted for a second or two, the old email continues to display, then the deleted email drops out, and shortly the new one displays, the whole process taking a bit over two seconds... to move from one email to the next, a process that used to be nearly instantaneous. No idea exactly when that changed, but it seems to be a process that's getting worse with time. Any ideas on what I might be able to do to get my original level of performance back? For what it's worth, this is a new machine, insanely fast compared to my older one, and Tbird is the only app where I'm encountering this kind of slowness issue. Everything else is astonishingly faster by comparison... but Tbird remains laggy and slow and I've no idea where to start looking for reasons for this. Don't even know what kind of information to post here that might be useful in diagnosing the issue - - tell me what's needed and I'll do my best to get it. Thanks in advance! I *really* don't want to change email clients after all this time!