So only when quick filter bar is active.

If you can still reproduce pleae file a bug report at https://bugzilla.mozilla.org/enter_bug.cgi?product=thunderbird

Hi Wayne Mery,

Thank you very much for your reply.

After further testing, I found that the issue is not actually caused by the quick filter bar being active. I initially thought that was the reason, but after observing carefully, it turns out the quick filter bar itself is not the root cause.

The real problem seems to be related to the distance between the horizontal scrollbar at the bottom of the message list window and the last email in the list. When they are too close, the scrollbar ends up overlapping the subject line of the last email.

How to reproduce the issue:

1. Switch to Compact View.

1. Make sure the message list has enough emails and enough columns so that a horizontal scrollbar appears.

1. Move the mouse near the bottom (close to the horizontal scrollbar). In this situation, it’s very easy to accidentally activate the scrollbar, which blocks part of the last email and makes it difficult — sometimes impossible — to select the last email.

I’ll prepare a more detailed report with screenshots and submit it through the bug report link you shared.

Thanks again for your help!