Block all connections and allow only few?

I have a mobile data card with limited traffic quota on it that i use to access internet on my laptop. I want to setup comodo firewall to block all applications that generate traffic, system or user installed, and allow only on few of them to access the internet, for example Firefox browser. What is the best way to do this?

Set the firewall to “custom ruleset” and then manually add the rules for the programs you wanna allow

I guess first i have to purge all application and global rules?

By default you only have rules for comodo and windows apps, so i think there is no need to purge them.
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