diff --git a/tools/tinderbox/build-seamonkey-util.pl b/tools/tinderbox/build-seamonkey-util.pl
index 474c535c3ab..44e4c0fb157 100644
--- a/tools/tinderbox/build-seamonkey-util.pl
+++ b/tools/tinderbox/build-seamonkey-util.pl
@@ -24,7 +24,7 @@ use Config;         # for $Config{sig_name} and $Config{sig_num}
 use File::Find ();
 use File::Copy;
 
-$::UtilsVersion = '$Revision: 1.352 $ ';
+$::UtilsVersion = '$Revision: 1.353 $ ';
 
 package TinderUtils;
 
@@ -900,8 +900,7 @@ sub BuildIt {
     # Bypass profile manager at startup.
     $ENV{MOZ_BYPASS_PROFILE_AT_STARTUP} = 1;
 
-    # Avoid debug assertion dialogs (win32)
-    $ENV{XPCOM_DEBUG_BREAK} = "warn";
+    $ENV{XPCOM_DEBUG_BREAK} = "$Settings::MozAssertBehavior";
 
     # Set up tag stuff.
     # Only one tag per file, so -r will override any -D settings.
diff --git a/tools/tinderbox/tinder-defaults.pl b/tools/tinderbox/tinder-defaults.pl
index 1072bbee92e..d43362b3e92 100644
--- a/tools/tinderbox/tinder-defaults.pl
+++ b/tools/tinderbox/tinder-defaults.pl
@@ -129,6 +129,11 @@ $MozConfigFileName = 'mozconfig';
 $UseMozillaProfile = 1;
 $MozProfileName = 'default';
 
+# This sets the value of the XPCOM_DEBUG_BREAK environment variable.  We
+# default to 'warn', which suppresses the assertion dialogs on Windows
+# and gives platform parity.  Use 'abort' for fatal assertions.
+$MozAssertBehavior = 'warn';
+
 #- Set these to what makes sense for your system
 $Make          = 'gmake';       # Must be GNU make
 $MakeOverrides = '';