I've been using Thunderbird for the last 11 years daily at home and at work. Generally, it has been a remarkably stable and pleasant ride.

I remember a few bumps around 08..2010 where I ran beta builds because of some bugs. Also, I used to have extensions that colorized patches and highlighted quotes/threads... but those eventually broke and disappeared.

So, right now I am running a stock Thunderbird with a few profile customizations that tweak fonts (colors and sizes). Hitting GMail (work) and Fastmail (home) servers every minute or so.

Go Thunderbird!