To add support for BitTorrent magnet links in the Firefox browser on a Linux system, you will need to install a plugin or extension that can handle magnet links. One option is to use the "Magnet Link Fixer" extension, which is available from the Firefox Add-ons website.
To install the "Magnet Link Fixer" extension:
Open the Firefox browser and go to the "Magnet Link Fixer" extension page: https://addons.mozilla.org/en-US/firefox/addon/magnet-link-fixer/
Click the "Add to Firefox" button.
When prompted, click "Add" to confirm the installation of the extension.
Restart Firefox for the changes to take effect.
Once the extension is installed, it should automatically handle magnet links in Firefox. When you click on a magnet link, the extension will prompt you to choose a BitTorrent client to open the link with. If you do not have a BitTorrent client installed, you will need to install one in order to download the file. Some popular BitTorrent clients for Linux include qBittorrent, Deluge, and Transmission.
Keep in mind that downloading files using BitTorrent can be a legal gray area, and you should be careful to only download files that are legal in your jurisdiction.