Using TB 52.6 on Windows 10 with recent updates. This looks to be the exact same thing as described in https://support.mozilla.org/en-US/questions/1033167 I suffered from this issue for quite a while previously, but resolved it by turning off 'Allow Windows Search to Search Messages' in general options Since last TB update (52?) the problem has returned, even though the Allow search options is still off My 'workaround' is every time TB freezes up I restart Windows search. As soon as the Service stops, TB unfreezes and I am good for another 30-60 minutes Tiresome Note: I have moved my profile from C: to D: drive AND have excluded all TB directories (executables, profiles) that I can find from Windows search. Assume a Windows search bug here, and I'm sure MS will jump right on it and fix it for me, and apologize for their mistake any time now, but I have been waiting a whole week....