This has taken awhile to trackdown. This started occuring within the last couple of updates.
I am using Thunderbird v17 and v16.1 of McAfee antivirus that is part of Internet security on Windows XP.
When I click on any item in Thunderbird, mcshield.exe immediately goes to close to 100% effectively freezing my machine until mcshield.exe returns to 0%. It does not matter if I am clicking on indicator that shows whether or not a message has been read, the junk mail indicator, clicking on the message to read it, or switching between folders.
Unless this problem is resolved immediately, I am going to start looking for another program to secure my PC.
The McAfee techinician did not find any problems.
Thunderbird's latest version has a problem. Turn off Email attachment scanning in SecurityCenter > Virus and Spyware Protection > Real Time Scanning > Settings
You are still protected if you save said attachments to the hard drive, they will then be scanned.
This thread has some insight on that - https://community.mcafee.com/thread/50903?start=0&tstart=0
Unfortunately, disabling the scanning of email attachments is not an acceptable solution. This use to work until one of the most recent McAfee updates.
This problem occurs even when there is NO attachment.
I would expect McAfee to fix this problem rather quickly. I view disabling the scanning of email attachments as a short-term work around. "Short-term" is to be taken as a fix is ready within the next 10 days.
If you want it fixed quickly make sure you have added your voice to the cases reported by contacting Tehcnical Support.