I developed this for my own needs but I don't see why I shouldn't share it!
Usage is very easy:
* Make sure you have installed an application capable of intercepting magnet: links. See https://en.wikipedia.org/wiki/Magnet_URI_scheme#Clients_table (even though this page may be more up-to-date: https://en.wikipedia.org/wiki/Comparison_of_BitTorrent_clients#Features_I)
* Open at least a magnet link manually and associate a default application to the protocol
* Now clicking the add-on button will open all magnet links in all open tabs and send them to the torrent client!
Let me know if you find any issues, this is my very first mod and is very early in development, it definitely needs more work ;)