diff --git a/mozilla/layout/generic/nsLineLayout.h b/mozilla/layout/generic/nsLineLayout.h
index 30022312820..04945a49992 100644
--- a/mozilla/layout/generic/nsLineLayout.h
+++ b/mozilla/layout/generic/nsLineLayout.h
@@ -160,7 +160,13 @@ protected:
 #define LL_LASTFLOATWASLETTERFRAME     0x00000080
 #define LL_CANPLACEFLOAT               0x00000100
 #define LL_LINEENDSINBR                0x00000200
-#define LL_LASTFLAG                    LL_LINEENDSINBR
+// The "soft-break" flag differs from the "hard-break" flag of <br>. The
+// "soft-break" means that a whitespace has been trimmed at the end of the line,
+// and therefore its width has not been accounted for (this width can actually be
+// large, e.g., if a large word-spacing is set). LL should not be misled into 
+// placing something where the whitespace was trimmed. See bug 329987.
+#define LL_LINEENDSINSOFTBR            0x00000400
+#define LL_LASTFLAG                    LL_LINEENDSINSOFTBR
 
   PRUint16 mFlags;
 
@@ -239,6 +245,16 @@ public:
     SetFlag(LL_LINEENDSINBR, aOn); 
   }
 
+  PRBool GetLineEndsInSoftBR() const 
+  { 
+    return GetFlag(LL_LINEENDSINSOFTBR); 
+  }
+
+  void SetLineEndsInSoftBR(PRBool aOn) 
+  { 
+    SetFlag(LL_LINEENDSINSOFTBR, aOn); 
+  }
+
   PRBool InStrictMode() const
   {
     return mCompatMode != eCompatibility_NavQuirks;
diff --git a/mozilla/layout/generic/nsTextFrame.cpp b/mozilla/layout/generic/nsTextFrame.cpp
index de7fa42cd9e..b1af9c21fd2 100644
--- a/mozilla/layout/generic/nsTextFrame.cpp
+++ b/mozilla/layout/generic/nsTextFrame.cpp
@@ -5417,7 +5417,7 @@ nsTextFrame::MeasureText(nsPresContext*          aPresContext,
             // Note: word-spacing or letter-spacing can make the "space" really
             // wide. But since this space is left out from our width, linelayout
             // may still try to fit something narrower at the end of the line.
-            // So on return (see below), we flag a break-after status to ensure
+            // So on return (see below), we flag a soft-break status to ensure
             // that linelayout doesn't place something where the "space" should
             // be.
             break;
@@ -5854,11 +5854,17 @@ nsTextFrame::MeasureText(nsPresContext*          aPresContext,
 #endif // IBMBIDI
     ? NS_FRAME_COMPLETE
     : NS_FRAME_NOT_COMPLETE;
-  if (endsInNewline || aTextData.mTrailingSpaceTrimmed) {
+  if (endsInNewline) {
     rs = NS_INLINE_LINE_BREAK_AFTER(rs);
-    if (endsInNewline) {
-      lineLayout.SetLineEndsInBR(PR_TRUE);
-    }
+    lineLayout.SetLineEndsInBR(PR_TRUE);
+  }
+  else if (aTextData.mTrailingSpaceTrimmed && rs == NS_FRAME_COMPLETE) {
+    // Flag a soft-break that we can check (below) if we come back here
+    lineLayout.SetLineEndsInSoftBR(PR_TRUE);
+  }
+  else if (lineLayout.GetLineEndsInSoftBR() && !lineLayout.GetEndsInWhiteSpace()) {
+    // Break-before a word that follows the soft-break flagged earlier
+    rs = NS_INLINE_LINE_BREAK_BEFORE();
   }
   else if ((aTextData.mOffset != contentLength) && (aTextData.mOffset == startingOffset)) {
     // Break-before a long-word that doesn't fit here