I found this in shortcuts.xhtml and also with installation of DE SeaMonkey 2.53.17 Beta 1 Pre Mozilla/5.0 (NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Firefox/91.0 SeaMonkey/2.53.17B1 Build 20230610113409 (normal user Profile), Default Classic Theme on German WIN10 64bit in Help

STR:

1. Launch SM Browser
2. F1 for Help
3. search Help for "Tastenkombinationen"
4. Click "Allgemeine Tastenkombinationen"
5. Below "Allgemeine Tastenkombinationen für SeaMonkey in table you find
   "Fokus auf Suchfeld Strg+F or Strg+K Cmd+F or Cmd+K Strg+F or Strg+K"
   » Expected: Strg+F does the same like Strg+K
   Actual: They do different 😥
6. Test on that help Page:
   » Strg+F will brig up focus to Page search
   Strg+K will brig up focus to HELP search

This difference should be mentioned clearly in Help

Additional Info

a) Also tested Mailnews with visible News List, News View, Folder View
» Strg+F will brig up focus to News Test search in News View
» Strg+K will brig up focus to News List search
b) Also tested Composer Normal View
» Strg+F will brig up focus to Page Search
» Strg+K will bring Hyperlink Dialog !!!
c) Also tested Address Books (1 Address Book Highlighted)
» Strg+F does Nothing
» Strg+K will bring up focus to Address Bock Search (for an entry)
d) Also tested Chatzilla (Caret in Input field)
» Strg+F Will search Postings Area
» Strg+K does Nothing
e) Probably that started long before 2.53