When starting Thunderbird (45.2.0) under Windows 8.1, after a few seconds TBird hangs with the message: Warning: Unresponsive script: A script on the page may be busy, or it may have stopped responding..... Script: chrome://msktbird/content/mail-msktbird_3.js:566 After several minutes it frees up for a while and then fails again. Obviously "chrome" is a misnomer, and if I look for a near match on the PC, I find: C:\Program Files\McAfee\MSK\chrome\msktbird_3.jar - 9th June 2015, size 20,221 It's the only file in there, so perhaps McAfee has mis-attributed it. Anyway I started a case with McAfee and they cannot find anything wrong. "Contact supplier" was all they could say.. They did try - re-installing etc. - but no difference.