Problem: Seamonkey/Firefox does not know by default how to handle downloaded files and magnet links.
Solution: Read AlienBob’s and someslack blogs regularly :) The instructions for Firefox work just fine for Seamonkey. So:
File associations: when a file is downloaded for the first time, right click on, choose
Open > Choose an application > Choose and point to
/usr/bin/xdg-open. Make sure to check “Remember my choice for file links”.
Magnet links: open
about:config, right click and choose
New > Boolean and paste the following:
false as its value. Then in
Open > Choose an application > Choose point to e.g.
/usr/bin/transmission-gtk. Do not point to
/usr/bin/xdg-open, or the browser will start opening an endless amount of tabs when you click on a magnet link next time.