Firefox addon blocked from agent by Google Safe Browsing service
I opened the browser console for other work, and saw that the Snowflake addon was looping with the errors "The resource at “https://snowflake-broker.bamsoftware.com/proxy” was blocked by Safe Browsing." and "Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://snowflake-broker.bamsoftware.com/proxy. (Reason: CORS request did not succeed)."
I worked around the problem by going to that URL in a new tab and clicking the "do it anyway" option when the warning appeared, and now the addon is looping normally with the "at client capacity" message. But bypassing/disabling Safe Browsing is obviously a non-starter for general users, so someone needs to determine why the agent URL was blacklisted by Google and get it cleared, or the Firefox addon will be effectively dead.
Addon version 0.0.5.