diff --git a/layout/generic/nsSelection.cpp b/layout/generic/nsSelection.cpp
index d11b0b8d83c..a6b14218603 100644
--- a/layout/generic/nsSelection.cpp
+++ b/layout/generic/nsSelection.cpp
@@ -3780,10 +3780,34 @@ Selection::GetIndicesForInterval(nsINode* aBeginNode, PRInt32 aBeginOffset,
   bool intervalIsCollapsed = aBeginNode == aEndNode &&
     aBeginOffset == aEndOffset;
 
+  bool doSearches = true;
+
   // Ranges that end before the given interval and begin after the given
   // interval can be discarded
   PRInt32 endsBeforeIndex;
-  if (NS_FAILED(FindInsertionPoint(&mRanges, aEndNode, aEndOffset,
+  PRInt32 beginsAfterIndex;
+
+  // Optimization: Check that we're not at/after the end first
+  PRInt32 cmp;
+  if (NS_FAILED(CompareToRangeEnd(aBeginNode, aBeginOffset,
+                                  mRanges[mRanges.Length() - 1].mRange,
+                                  &cmp))) {
+    return;
+  } else if (cmp == 1) {
+    *aEndIndex = mRanges.Length();
+    return;
+  } else if (cmp == 0) {
+    beginsAfterIndex = mRanges.Length() - 1;
+    if (!intervalIsCollapsed) {
+      endsBeforeIndex = beginsAfterIndex + 1;
+    } else {
+      endsBeforeIndex = beginsAfterIndex;
+    }
+    doSearches = false;
+  }
+
+  if (doSearches &&
+      NS_FAILED(FindInsertionPoint(&mRanges, aEndNode, aEndOffset,
                                    &CompareToRangeStart,
                                    &endsBeforeIndex))) {
     return;
@@ -3807,14 +3831,12 @@ Selection::GetIndicesForInterval(nsINode* aBeginNode, PRInt32 aBeginOffset,
   }
   *aEndIndex = endsBeforeIndex;
 
-  PRInt32 beginsAfterIndex;
-  if (NS_FAILED(FindInsertionPoint(&mRanges, aBeginNode, aBeginOffset,
+  if (doSearches &&
+      NS_FAILED(FindInsertionPoint(&mRanges, aBeginNode, aBeginOffset,
                                    &CompareToRangeEnd,
                                    &beginsAfterIndex))) {
     return;
   }
-  if (beginsAfterIndex == (PRInt32) mRanges.Length())
-    return; // optimization: all ranges are strictly before us
 
   if (aAllowAdjacent) {
     // At this point, one of the following holds: