--- a/layout/generic/nsTextFrame.cpp
+++ b/layout/generic/nsTextFrame.cpp
@@ -9629,27 +9629,20 @@ static void TransformChars(nsTextFrame* 
     } else {
       // Should not happen (see assertion above), but as a fallback...
       aOut.Append(fragString);
     }
   }
 }
 
 static bool
-LineEndsInHardLineBreak(nsTextFrame* aFrame)
-{
-  nsIFrame* lineContainer = FindLineContainer(aFrame);
-  nsBlockFrame* block = do_QueryFrame(lineContainer);
-  if (!block) {
-    // Weird situation where we have a line layout without a block.
-    // No soft breaks occur in this situation.
-    return true;
-  }
+LineEndsInHardLineBreak(nsTextFrame* aFrame, nsBlockFrame* aLineContainer)
+{
   bool foundValidLine;
-  nsBlockInFlowLineIterator iter(block, aFrame, &foundValidLine);
+  nsBlockInFlowLineIterator iter(aLineContainer, aFrame, &foundValidLine);
   if (!foundValidLine) {
     NS_ERROR("Invalid line!");
     return true;
   }
   return !iter.GetLine()->IsLineWrapped();
 }
 
 nsIFrame::RenderedText
@@ -9657,40 +9650,62 @@ nsTextFrame::GetRenderedText(uint32_t aS
                              uint32_t aEndOffset,
                              TextOffsetType aOffsetType,
                              TrailingWhitespace aTrimTrailingWhitespace)
 {
   NS_ASSERTION(!GetPrevContinuation(), "Must be called on first-in-flow");
 
   // The handling of offsets could be more efficient...
   RenderedText result;
+  nsBlockFrame* lineContainer = nullptr;
   nsTextFrame* textFrame;
   const nsTextFragment* textFrag = mContent->GetText();
   uint32_t offsetInRenderedString = 0;
   bool haveOffsets = false;
 
+  Maybe<nsBlockFrame::AutoLineCursorSetup> autoLineCursor;
   for (textFrame = this; textFrame;
        textFrame = static_cast<nsTextFrame*>(textFrame->GetNextContinuation())) {
     if (textFrame->GetStateBits() & NS_FRAME_IS_DIRTY) {
       // We don't trust dirty frames, especially when computing rendered text.
       break;
     }
 
     // Ensure the text run and grab the gfxSkipCharsIterator for it
     gfxSkipCharsIterator iter =
       textFrame->EnsureTextRun(nsTextFrame::eInflated);
     if (!textFrame->mTextRun) {
       break;
     }
     gfxSkipCharsIterator tmpIter = iter;
 
+    // Whether we need to trim whitespaces after the text frame.
+    bool trimAfter;
+    if (!textFrame->IsAtEndOfLine() ||
+        aTrimTrailingWhitespace !=
+          TrailingWhitespace::TRIM_TRAILING_WHITESPACE) {
+      trimAfter = false;
+    } else if (nsBlockFrame* thisLc =
+               do_QueryFrame(FindLineContainer(textFrame))) {
+      if (thisLc != lineContainer) {
+        // Setup line cursor when needed.
+        lineContainer = thisLc;
+        autoLineCursor.reset();
+        autoLineCursor.emplace(lineContainer);
+      }
+      trimAfter = LineEndsInHardLineBreak(textFrame, lineContainer);
+    } else {
+      // Weird situation where we have a line layout without a block.
+      // No soft breaks occur in this situation.
+      trimAfter = true;
+    }
+
     // Skip to the start of the text run, past ignored chars at start of line
-    TrimmedOffsets trimmedOffsets = textFrame->GetTrimmedOffsets(textFrag,
-       textFrame->IsAtEndOfLine() && LineEndsInHardLineBreak(textFrame) &&
-       aTrimTrailingWhitespace == TrailingWhitespace::TRIM_TRAILING_WHITESPACE);
+    TrimmedOffsets trimmedOffsets =
+        textFrame->GetTrimmedOffsets(textFrag, trimAfter);
     bool trimmedSignificantNewline =
         trimmedOffsets.GetEnd() < GetContentEnd() &&
         HasSignificantTerminalNewline();
     uint32_t skippedToRenderedStringOffset = offsetInRenderedString -
         tmpIter.ConvertOriginalToSkipped(trimmedOffsets.mStart);
     uint32_t nextOffsetInRenderedString =
         tmpIter.ConvertOriginalToSkipped(trimmedOffsets.GetEnd()) +
         (trimmedSignificantNewline ? 1 : 0) + skippedToRenderedStringOffset;