diff --git a/chrome.manifest b/chrome.manifest
index 58980a15..2e91a39e 100644
--- a/chrome.manifest
+++ b/chrome.manifest
@@ -50,7 +50,7 @@ override chrome://treestyletab/skin/Linux-tabs-on-bottom.css	chrome://treestylet
 override chrome://treestyletab/skin/square/platform.css	chrome://treestyletab/skin/square/Darwin.css	os=Darwin
 override chrome://treestyletab/skin/square/platform.css	chrome://treestyletab/skin/square/Linux.css	os=Linux
 override chrome://treestyletab/skin/square/platform.css	chrome://treestyletab/skin/dummy.css	os=WINNT
-override chrome://treestyletab/skin/square/disable-closebox-bg.css	chrome://treestyletab/skin/dummy.css	os=Linux appversion>=29.0a1
+override chrome://treestyletab/skin/square/disable-closebox-bg.css	chrome://treestyletab/skin/dummy.css	os=Linux appversion>=29.0b4
 
 override chrome://treestyletab/skin/metal/platform.css	chrome://treestyletab/skin/metal/Darwin.css	os=Darwin
 override chrome://treestyletab/skin/metal/platform.css	chrome://treestyletab/skin/dummy.css	os=WINNT