You can force a manual download of the certificate revocation list.
First of all, each vendor of certificates provides its own CRL. The address of the CRL can be found in the certificate. So, depending on which vendor issued the certificate of your contact, you may need to add more CRLs.
I'll describe the procedure:
First, look in
Tools -> Properties, Advanced, Certificates. Click on "Certificates...", there select the "Certificates of other people" tab and you'll get a list of all certificates of your contacts.
Double click a certificate, select "Details"
Under "Certificate Layout", you'll find an entry "Extensions" with an subentry, holding urls to download the crl.
Copy one of these urls to clipboard. For COMODO it's
Close this window and the certificate manager, back in properties, click on "CRLs...", select "Import" and paste the copied url.Note, that the automatic download of the CRL won't work, too!!
It seems to be also known to the Mozilla people...
To force a manual update, you have to click "Update" here.
I'm using a localized version of Thunderbird, so my translated names may differ from the original ones.