88.0b1 displays Intel user agent on Arm Mac

I am running the 88.0b1 universal binary for Intel and Arm, on a Macbook Pro with Apple silicon (M1 Arm). When I send a message, Thunderbird creates the following User-Agent header.

User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:88.0)
Gecko/20100101 Thunderbird/88.0

As you can see, it reports Intel even though I am on Arm. Is there a way to find out if it is somehow running the Intel version under Rosetta2?

If it is really running the Intel version, then maybe Thunderbird is using some sort of Intel-based intermediate launcher that causes the Intel version of the application to be launched. If it is running the Arm version, then Thunderbird is reporting an incorrect user agent string.