Bug in interaction between uMatrix and Snowflake (snowflake-webextension)

Error in Snowflake debug console, caused by a line in vapi-background.js in uMatrix:

Unchecked lastError value: Error: First-Party Isolation is enabled, but the required 'firstPartyDomain' attribute was not set.

The uMatrix setting causing this error is:

Spoof HTTP referrer string of third-party requests, when set to true.

This is a bug either in Snowflake, or uMatrix.