Does dragging a URL to SeaMonkey's icon or using Right Click>Open with>SeaMonkey work???
I can't get that far . . . somewhat "moot" at this point, SM was what I was hoping would get me away from TFF, but, because it is even "older" appearing to web sites, it never got me where I wanted it, never got it to be what it was before . . . full-featured browser, etc.
With the Webkit option to TFF, for the few things I can't get with WK, I can briefly launch TFF . . . . In SM it isn't responding to attempts to un-check "browser" and "email" as default for SM . . . and isn't responding to attempts to un-check "check this every time" option . . . I tried to get to "preferences" but with the drop-down menu open, nothing happens . . . and then it goes "un-responsive" . . . but, right now, it isn't "mission critical" . . . it's just one of those things I'd like to get working . . . at some point.
Since in the past I found Safari to "not work" I never got it totally set up and/or thrashed through . . . right now, trying to explore the params of Safari . . . .