Yeap. Full path and tixati exe with param.

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\magnet]
"URL Protocol"=""
@="URL:torrent magnet link"
"Content Type"="application/x-magnet"

[HKEY_CLASSES_ROOT\magnet\DefaultIcon]
@=""C:\Program Files\tixati\tixati.exe",1"

[HKEY_CLASSES_ROOT\magnet\shell]
@="open"

[HKEY_CLASSES_ROOT\magnet\shell\open]
"FriendlyAppName"="Tixati"

[HKEY_CLASSES_ROOT\magnet\shell\open\command]
@=""C:\Program Files\tixati\tixati.exe" "%1""

There is no need to reinstall Tixati. It has option to associate link/protocol. It works with Firefox.
Edge and Opera are ignoring magnet links.

In windows 10 magnet links doesn't work in 41/42. If i hit magnet link windows gives me only option to use windows store app. Firefox works.

ps: i tried rewriting local date and editing reg hklm for protocol magnet.