Why would you reinstall? You say nothing about problems integration with the operating system, so a reinstall would be most unlikely to do anything useful at all. I will say despite you "liking" whatever version you are using, the most recent release is the one with the fixes for the security faults that are found in all software almost on a daily basis. They are listed [https://www.mozilla.org/en-US/security/known-vulnerabilities/thunderbird/ here ]and while all may not affect you, enough would that you run an ever greater risk of having your system compromised the longer you go without an update. My understanding is you are actually an ATT customer and as such your mail service is provided by yahoo. Sometime late last year Yahoo ceased to asllow the use of a normal password to access mail using mail clients. Now you must use a mailkey. This is the link to the ATT web site where they offer instructions on creating such https://www.att.com/support/article/email-support/KM1240308/ Once you have the mailkey, you replace the password in Thunderbird with the mailkey.