Currently impossible to block Javascript on accounts.google.com if one is using UMatrix.
If you resort to blocking Javascript from within the browser itself then simply having UMatrix enabled in the browser breaks that blocking. It does not matter whether UMatrix setting for scripts for accounts.google.com is red or green. The browser will still run the javacript.
The same thing occurs if one removes the javascript blocking from the browser and simply relies on setting in the UMatrix to determine whether javascript for accounts.google.com are allowed or not. The browser still runs the javascript.
If you attempt to login to gmail.com and have enabled blocking of javascript on accounts.google.com and it is working properly, then should see the older style account login for gmail, the one with the rectangular boxes rather than the undelined fields.
It does not. You still get the newer login screen