How to connect Motrix download manger with Vivaldi?

[EpicMaker]

I tried to connect Motrix download manger with Vivaldi using their open source extension

https://github.com/gautamkrishnar/motrix-webextension

but it only saves when i am using Save as option only , so how to make it the default download manger ??

and this is Motrix download manger btw
https://motrix.app