Deck Importer Extension
The deck importer is a small Firefox add-on. You're on another site looking at a decklist, you click the OpenRift icon in the toolbar, and the deck lands on OpenRift's import page with its name and source link filled in. No copying, no export step, and it works whether or not you're signed in.
Install it
Mozilla signs the add-on, but I host it myself instead of listing it on addons.mozilla.org, so installing takes one extra confirmation.
Download the deck importer for Firefox
Updates take care of themselves. Firefox checks for a newer signed build roughly once a day, so you only ever do this once.
Import a deck
Signed out, the deck is saved in your browser and moves to your account the next time you sign in.
What it can read
What it can access
Only the tab you're on, only in the moment you click. It asks for no list of sites, so it can't run in the background, and it never sees your browsing history. Reading happens inside the page, and the only thing that leaves is the deck itself, as part of the import link that opens.