Where does the manual "Update Sieve" update from ?

I installed the latest (2017-07-16) 0.9.8.54 version of imagus.xpi from "Imagus Archive". Here: https://drive.google.com/drive/folders/0Bx8fnUCX4W2IUTNPT0s2eUFDQms

Removed one of the 260 Sieve rules. Clicked the "Update Sieve" button (The down arrow). Result - The removed rule "returned" as expected. It seems that everything is working fine.

So does that means that Google Drive "returned" to work as a web-server ?

I'm asking this because some months ago the dev wrote : "Clicking the update button won't work, since Google Drive doesn't work as a web-server anymore. Unfortunately, I don't have the time to migrate to somewhere else." https://www.reddit.com/r/imagus/comments/5511wo/sieve_wont_update/d88mdw9/

Thanks in advance.

Pale Moon 27.4.0 Win 7 x64