As of now, SeaMonkey has switched to the same "OpenSearch" system as
Firefox, so the previous .src/.png format for search plugins has been
de-supported for those we provide by default and we're only supporting
.xml search plugins in the defaults and locales from now on in the
SeaMonkey 2.1 series and above. (The old "Sherlock" format still works
when installed by users into their profile but we won't ship such
plugins in the application.)
If there's no good reason for providing your own search plugins, please
don't add any for now, we'll fetch any that are in list.txt but not
existing in your locale from en-US instead. We also don't want any
locale to ship more than 5 search plugins for the moment.
Note that compared to Firefox, we don't have eBay or amazon in the
default list right now, and we have subtle changes in the Google and
possibly Yahoo ones to not use any tags that are for special Firefox
contracts, so be careful when you may want to port any search plugins
from Firefox, as we are not allowed to use such tags.