To diagnose problems with Thunderbird, try one of the following:

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Thanks for the info I don't think its other software, as all the apps and extensions are exactly the same as on my other PCs, but Ill have a look.

Is there any way to back up my settings, the design of Thunderbird, spelling, address book etc. Is there an extension that will do this?

Thanks

Is there any way to back up my settings, the design of Thunderbird, spelling, address book etc.

Backup the entire Thunderbird profile. https://support.mozilla.org/kb/profiles-where-thunderbird-stores-user-data#w_backing-up-a-profile

Is there an extension that will do this?

ImportExportTools NG seems to do backups. I haven't tried it. https://addons.thunderbird.net/en-US/thunderbird/addon/importexporttools-ng/

That worked, thanks An Add on was slowing it down, now to find it

It was the having more than 1 calander apps at one time

It was the having more than 1 calander apps at one time

Calendars, or add-ons? Which ones?

Can't remember, I downloaded 3

My Thunderbird was very slow --- this problem has come and gone many times. Lately is was very slow in moving files between directories. Today I did these two things and it works great so far: (1) Go to Tools | Clear Recent History and select Everything. (2) Increase the cache size. Go to Tools | Options | General | Disk Space and Check "Overide automatic cashe mangement" and change the number in "Use up to --- MB of space for the cache" to 1024.

Thanks for the info.

Thunderbird works fine on all other Windows 10 PCs.

It works now, but if I install Google Calander or the app to remove the Calander icon from the top bar, it slows down, so writing emails takes a long time

I tried all the different Calander apps, they all do this.

Will try this.

Thanks

Anyone else know how I can fix this problem?

Thunderbird works fine on all PC's, but on this one laptop, whenever I install Calander, it stops working. Tried all different Google calendar apps, tried reinstalling, tried everything.

thanks