Foreword: This issue a year long now. I read many forums at the internet. I did not found any useful solutions on the net yet. Officials are repeating the same good old advices like update, turn off, safe mode, but nothing REAL. I was smiling about this problem and did not understand why my colleagues and clients going mad because of this, till suddenly it started to happen with my computer as well and its worst and worst day by day. Same issues: - freeze at activity (freeze when open, freeze when delete, freeze when moving letters from one folder to another), - total freeze with sudden crash of TB, task manager dont help, only restarting OS works as the only solution. Our company operates many computers and managing other companies PC's as well. We have faced with this problem in the following environments: - upgraded win10 / clean install win 10 - Home 64bit, Pro 64 bit - English and other languages as well - Intel and AMD motherboards as well - desktop and notebooks as well - Brand PC's and self made PC's as well - On "cheap" models and high-end models as well - Thunderbird versions through 38.xx to 45.xx - many different AV softwares environment (from none trough win defender to some 6-8 different major Av companies) Done all the necessary things all others did too: - Win 10 is fully updated (anniversary update) - TB is the newest 45.xx - no addons, or removed or turned off - Some officials says Win defender is the problem: NO it is checked by community, dead end, solutions are not works - Some officials says Win firewall is the problem: NO it is checked by community, dead end, solutions are not works - Some officials says AV software is the problem: NO it is checked by community, dead end, solutions are not works. When some unistalled AV, problems are still exists. One personal note: It is highly possible that it is NOT because of AV software since there are lots of them on the market and as I read complaints there are complaints with all kind of AV softwares. (99% were not Norton users) Personally I used ESET before, now use AVAST. Both are non-free versions. I still have same issue on my PC, problems still exists. Checked win and TB safe mode. It was okay, but problem came back immediately after we went back to normal operation. Not tried yet: - CC cleaner and other "fixing" softwares, since they are sometimes deleting too much - the deleting msf files solution (we will do it today, some says it is a solution that works for only a few days) Any idea somebody? Personal note to "officials" 1. Pls DONT TELL us to shut down AV software, when tons of spam letters coming daily, port scans, virus attacks are happening daily. We have to defend ourselves. Not to mention surfing naked on the internet is not healthy. 2. I dont want to save Microsoft, since I am sure they caused this whole situ. Our Linux PC's works fine with Thinderbird. BUT also I am really sad that this Thunderbird issue came up first in Aug-Sept 2015 and now we are in September 2016. STILL Mozilla guys came up with nothing really useful advice that shows you are dedicated some time to investigate the issue. Just repeating the good old advices like update your sw, etc. This issue came up first with TB ver 38.xx now we are at 45.xx Still no real solution.