Use the URI component encoded version of the board name internally.

src/General/Get.coffee

@@ -1,7 +1,7 @@
 Get =
   threadExcerpt: (thread) ->
     {OP} = thread
-    excerpt = ("/#{thread.board}/ - ") + (
+    excerpt = ("/#{decodeURIComponent thread.board.ID}/ - ") + (
       OP.info.subject?.trim() or
       OP.commentDisplay().replace(/\n+/g, ' // ') or
       OP.file?.name or

src/main/Main.coffee

@@ -323,6 +323,7 @@ Main =
 
       for threadRoot in $$(s.thread, board)
         boardObj = if (boardID = threadRoot.dataset.board)
+          boardID = encodeURIComponent boardID
           g.boards[boardID] or new Board(boardID)
         else
           g.BOARD