Hello there Alana.Walsh. We have read your message. We try to help you. What version of Thunderbird do you use? The workaround from Avast is the good way to accept. Copy the URL. Go to the dashboard on your pc or laptop. Click the menu button to the settings. Under this button menu click Add exception and the window will appear to save this adres. When clicking add exception the job for saving the adres is there and finished . When using this new adres to bypass. Is the best way for short time use. Avast will replace the certificates automatically if your Avast antivirus is validated. Or issues from Avast security site are solved. If you are planning to insert a certificate into Thunderbird. Open Thunderbird. ... Click on Advanced > Certificates > View Certificates. On the Certificate Manager screen click the Your Certificates tab. ... Browse to your certificate and enter the PFX certificate password to import it to Thunderbird. Click OK to exit the Certificate Manager. If you are having a certificate to replace. Choose right click on the mouse with the cursor on the certificate. Install PFX certificate. The installation wizard will continue to install your certificate s. If you are not one of these persons that can insert or fix a certificate for both of them Thunderbird or Avast turn of the SSL function in thunderbird that stops the SSL pop ups. Greetings Firefox volunteer