In Windows, delete the entry in Windows Environment:
In Windows Settings, search for environment | Choose "Edit system environment variables"
Select "Environment Variables" and under "System Variables," DELETE the environment variable MOZ_NO_REMOTE
It doesn't matter whether the variable value is set to 0 or to 1 — the mere presence of the variable appears to cause this problem, including if you try to send an email from Thunderbird from any browser.
In Windows, delete the entry in Windows Environment:
In Windows Settings, search for environment | Choose "Edit system environment variables"
Select "Environment Variables" and under "System Variables," DELETE the environment variable MOZ_NO_REMOTE
It doesn't matter whether the variable value is set to 0 or to 1 — the mere presence of the variable appears to cause this problem, including if you try to send an email from Thunderbird from any browser.