I grepped the Thunderbird source code, and the only references I could find are for integration with Facebook's now-discontinued XMPP chat system. I also can't find any references to those IP addresses.

The IP range seems correct (https://whois.arin.net/rest/net/NET-157-240-0-0-1/pft?s=157....), but that doesn't mean there may be some other error. I started Thunderbird and it's not connecting to any Facebook domain or IP.

Unfortunately the claim doesn't contain any details other than "I blocked Facebook and my email stopped working". I don't know what situation the author encountered, but the bombastic claim of "Thunderbird is spying you" is completely unproven.