If you use jaxx or exodus it is possible to import the ETH privatkey to MetaMask and do the registration from there.
It is a god idea to download vmware or virtualbox and install a clean linux distro like xubuntu. From there you can install the brave browser and metamask. This way you lower the risk of someone steals your keys.

After the xubuntu installation you can open the terminal and follow this commands.

sudo apt-get update
sudo apt-get upgrade
sudo apt install snapd
snap install brave --beta

After installing brave you go to extensions within the Brave Browser and activate MetaMask.

I am NOT an expert on cybersecurity. This a way of doing things that I think is better then using the same OS for everything from surfing the web and managing privatkeys.