Are you a McAfee user?

https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues#McAfee

I'm being told by Mcafee that I do not have anti spam or firewall pretection. I have Mcafee thru my cable company.

OK, did you follow the instructions in the previous link to disable email attachment scanning and scanning of the TB profile folder?

Could not find in McAfee where dropdowns were such as 'tools'..etc....

thanks you for trying to help..Perhaps you could dirct me to these dropdowns ?

I don't have a McAfee product installed, but I'm sure you can get the necessary guidance on the McAfee website.

OK..problem resolved. What was needed to be done: In McAfee click on 'Navigation' Click on 'Real Time Scanning' Uncheck 'Email attachments' Check 'Minimize the effect on my PC's speed, even though the scan is less thorough'.

Since I made these changes, my thunderbird mozilla email is fast with no disruptions. And in spite of the 'less thorough' statement, scans are thorough.