I see what you're saying, because it's a component URL I don't get the 404 page?

Actually in that case what i want is for it to redirect to com_kunena wherever it sees com_fireboard.

When you say "in the database," which table are you referring to?

You don't get 404 page from JoomSEF because it's not a SEF URL.

You will probably need to create custom RewriteRule in your .htaccess file to redirect URLs with option=com_fireboard to URL with option=com_kunena.

I mean the URLs that are displayed on JoomSEF's Manage SEF URLs page. Those are stored in jos_sefurls table.