At <de.comm.software.mozilla.browser> User Wolfgang Kefurt told in "SM 2.39 Lesezeichen suchen nicht vorhanden?" that since SM 2.39 the "Search bookmarks" search string input line is missing.
With SeaMonkey 2.39 final Mozilla/5.0 (Windows NT 6.1; WOW64; rv:42.0 from official download area) Gecko/20100101 Firefox/42.0 Build 20151103191810 (Classic Theme) on German WIN7 64bit I see that "Search bookmarks" search string input line appearing and vanishing with the menu bar of the bookmarks Manager (as expected), but on Mac (if I understood everything correctly) the Menu bar is part of the SeaMonkey Window and not of the Bookmarks Editor Dialog, works completely different.
It's not proved, but I am pretty sure that this problem came up with fix for "Bug 1153577 - Users should be able to hide the menubar and show it with the ALT key"
Steps how to reproduce on MAC:
1. Launch Browser
2. Menu 'Bookmarks → Manage bookmarks'
Expected: "Search bookmarks" search string input line visible
bug: No search
Probably better Component
Mozillazine thread: http://forums.mozillazine.org/viewtopic.php?f=40&t=2973629
Marking as New.
DUP of Bug "1224907 - Bookmarks Manager Search missing in Mac Menu Bar"
*** This bug has been marked as a duplicate of bug 1224907 ***