When composing message, keyboard response is intermittently, but frequently slow. I can type ahead many characters, then suddenly the text "catches up" and I can type a few words normally and then another type-ahead lag. This happens frequently enough to make Thunderbird barely usable. Two workstations in the office have Thunderbird, both are Windows 7. This one has this problem consistently, the other does not appear to have the problem. I have tried uninstalling and reinstalling Thunderbird, altering the cache settings, etc. Any ideas on this problem? Conflicts with other programs? Email composing settings? Update: after some browsing, it seems that Harald Oehlmann posted to bug https://bugzilla.mozilla.org/show_bug.cgi?id=942610 on 2015-08-26 00:32:11 PDT with the same phenomenon, including the compose-window focus loss. Haven't come across resolution yet. BTW - I'm running Thunderbird 38.5.1 on Windows 7, the only add-on I have is Lightning. I am using spell checker.