You downloaded, installed and launched Thunderbird 91.0 from Thunderbird or is this a distribution version?
Bug 1725655 Comment 1 Edit History
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You downloaded, installed and launched Thunderbird 91.0(beta) from Thunderbird or is this a distribution version? Also, your Troubleshooting Information shows 91.0b3. The last beta in that series is 91.0b6, which will update to 92.0b1.