Thunderbird is excruciatingly slow - in every operation (I feel it most when compositing, but even just making my way through menus is sloooow). It feels like low memory, but I have 18gB or more of free RAM in Windows 10, and nothing else is running slowly.

What could I do to speed it up, as I am seriously considering switching email client, but don't know of anything as good?

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    Is there some ongoing operation, e.g. antimalware scan? Some scanners are incompatible with some email clients. Temporarily turn off AV suite, and , if problem goes away, try a different brand. – DrMoishe Pippik Aug 26 '20 at 17:14
  • Truning off Avast seemed to improve things slightly, but still not aceptable. Typing during compose and nothing seems to happen, then the text shows up after a delay .... (+1 though, for a good suggestion) – Mawg says reinstate Monica Aug 27 '20 at 5:49
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    @MawgsaysreinstateMonica slowness while typing describes a known issue with early version 78. You will want to update to 78.2.2 or higher (current version is 78.3.1). Regarding Avast, it certainly can cause issues*. But you don't need to turn it off, you can exclude parts of Avast that are affecting Thunderbird. * wiki.mozilla.org/… – wsmwk Sep 26 '20 at 11:12
  • That seems to have done the trick. One week later and things seem better. If you post that as an answer, I will accept it. Thanks for your help – Mawg says reinstate Monica Oct 2 '20 at 7:55

Could be lots of things, including hardware. Suggest you review https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems and post your results


Open Task Manager (alt-ctrl-delete) and look at your processes. The culprit could be thunderbird or another program that is hogging all your disk usage, cpu, and/or RAM.

If that doesn't work, reinstall thunderbird.

  • Over 18gNB free RAM, CPU at ubder 50%, maybe 20% free disk space from 3tB. Reinstalling is a last resort, unless you can tell me how to save my config. Thanks for the advice, though :-) – Mawg says reinstate Monica Aug 27 '20 at 5:46

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