You people need to read and understand the "law of diminishing returns". You had a good product years ago and it's been slowly going down hill by adding silly icons, flags, colors, etc. You're obviously running out of ideas so you are now just adding a lot of fluff that simply wastes resources. So STOP trying to add new, worthless features to Thunderbird email and just focus on bugs!! The latest version is slow and has crashed several times in 2 days with the popup that says "sorry".
One of the latest features you added is to make unread messages BOLD and then UNBOLD when you click on them. What a waste of CPU cycles. When plowing thru junk mail, I used to be able to quickly delete messages but now the BOLD/UNBOLD flipping makes the process slow and cumbersome.
Maybe you should make a no-frills version without all the crap for those who prefer speed and efficiency.