pkgdepend fails when there is no RPATH as /usr/lib/firefox/ isn't
default search path for libraries.

Note that it's not problem for Firefox itself which can cope with it.

--- firefox-153.0/build/moz.configure/flags.configure
+++ firefox-153.0/build/moz.configure/flags.configure
@@ -455,7 +455,7 @@
     if target.kernel == "WINNT":
         return []
     if target.kernel == "SunOS":
-        return [f"-L{dist}/bin"]
+        return [f"-L{dist}/bin", "-Wl,-R,$ORIGIN"]
     if target.os == "WASI":
         return []