--- a/gfx/thebes/gfxTextRun.cpp
+++ b/gfx/thebes/gfxTextRun.cpp
@@ -862,23 +862,27 @@ gfxTextRun::BreakAndMeasureText(uint32_t
 
     Range bufferRange(aStart, aStart +
         std::min<uint32_t>(aMaxLength, MEASUREMENT_BUFFER_SIZE));
     PropertyProvider::Spacing spacingBuffer[MEASUREMENT_BUFFER_SIZE];
     bool haveSpacing = aProvider && (mFlags & gfxTextRunFactory::TEXT_ENABLE_SPACING) != 0;
     if (haveSpacing) {
         GetAdjustedSpacing(this, bufferRange, aProvider, spacingBuffer);
     }
-    bool hyphenBuffer[MEASUREMENT_BUFFER_SIZE];
+    AutoTArray<bool, 4096> hyphenBuffer;
     bool haveHyphenation = aProvider &&
         (aProvider->GetHyphensOption() == StyleHyphens::Auto ||
          (aProvider->GetHyphensOption() == StyleHyphens::Manual &&
           (mFlags & gfxTextRunFactory::TEXT_ENABLE_HYPHEN_BREAKS) != 0));
     if (haveHyphenation) {
-        aProvider->GetHyphenationBreaks(bufferRange, hyphenBuffer);
+        if (hyphenBuffer.AppendElements(bufferRange.Length(), fallible)) {
+            aProvider->GetHyphenationBreaks(bufferRange, hyphenBuffer.Elements());
+        } else {
+            haveHyphenation = false;
+        }
     }
 
     gfxFloat width = 0;
     gfxFloat advance = 0;
     // The number of space characters that can be trimmed or hang at a soft-wrap
     uint32_t trimmableChars = 0;
     // The amount of space removed by ignoring trimmableChars
     gfxFloat trimmableAdvance = 0;
@@ -891,36 +895,51 @@ gfxTextRun::BreakAndMeasureText(uint32_t
 
     Range ligatureRange(aStart, end);
     ShrinkToLigatureBoundaries(&ligatureRange);
 
     uint32_t i;
     for (i = aStart; i < end; ++i) {
         if (i >= bufferRange.end) {
             // Fetch more spacing and hyphenation data
+            uint32_t oldHyphenBufferLength = hyphenBuffer.Length();
             bufferRange.start = i;
             bufferRange.end = std::min(aStart + aMaxLength,
                                        i + MEASUREMENT_BUFFER_SIZE);
+            // For spacing, we always overwrite the old data with the newly
+            // fetched one. However, for hyphenation, hyphenation data sometimes
+            // depends on the context in every word (if "hyphens: auto" is set).
+            // To ensure we get enough information between neighboring buffers,
+            // we grow the hyphenBuffer instead of overwrite it.
+            // NOTE that this means bufferRange does not correspond to the
+            // entire hyphenBuffer, but only to the most recently added portion.
+            // Therefore, we need to add the old length to hyphenBuffer.Elements()
+            // when getting more data.
             if (haveSpacing) {
                 GetAdjustedSpacing(this, bufferRange, aProvider, spacingBuffer);
             }
             if (haveHyphenation) {
-                aProvider->GetHyphenationBreaks(bufferRange, hyphenBuffer);
+                if (hyphenBuffer.AppendElements(bufferRange.Length(), fallible)) {
+                    aProvider->GetHyphenationBreaks(
+                        bufferRange, hyphenBuffer.Elements() + oldHyphenBufferLength);
+                } else {
+                    haveHyphenation = false;
+                }
             }
         }
 
         // There can't be a word-wrap break opportunity at the beginning of the
         // line: if the width is too small for even one character to fit, it
         // could be the first and last break opportunity on the line, and that
         // would trigger an infinite loop.
         if (aSuppressBreak != eSuppressAllBreaks &&
             (aSuppressBreak != eSuppressInitialBreak || i > aStart)) {
             bool atNaturalBreak = mCharacterGlyphs[i].CanBreakBefore() == 1;
             bool atHyphenationBreak = !atNaturalBreak &&
-                haveHyphenation && hyphenBuffer[i - bufferRange.start];
+                haveHyphenation && hyphenBuffer[i - aStart];
             bool atBreak = atNaturalBreak || atHyphenationBreak;
             bool wordWrapping =
                 aCanWordWrap && mCharacterGlyphs[i].IsClusterStart() &&
                 *aBreakPriority <= gfxBreakPriority::eWordWrapBreak;
 
             if (atBreak || wordWrapping) {
                 gfxFloat hyphenatedAdvance = advance;
                 if (atHyphenationBreak) {

--- a/layout/generic/nsTextFrame.cpp
+++ b/layout/generic/nsTextFrame.cpp
@@ -3627,17 +3627,18 @@ PropertyProvider::GetHyphenationBreaks(R
     if (run.IsSkipped()) {
       // Check if there's a soft hyphen which would let us hyphenate before
       // the next non-skipped character. Don't look at soft hyphens followed
       // by other skipped characters, we won't use them.
       allowHyphenBreakBeforeNextChar =
         mFrag->CharAt(run.GetOriginalOffset() + run.GetRunLength() - 1) == CH_SHY;
     } else {
       int32_t runOffsetInSubstring = run.GetSkippedOffset() - aRange.start;
-      memset(aBreakBefore + runOffsetInSubstring, false, run.GetRunLength()*sizeof(bool));
+      memset(aBreakBefore + runOffsetInSubstring, false,
+             run.GetRunLength() * sizeof(bool));
       // Don't allow hyphen breaks at the start of the line
       aBreakBefore[runOffsetInSubstring] = allowHyphenBreakBeforeNextChar &&
           (!(mFrame->GetStateBits() & TEXT_START_OF_LINE) ||
            run.GetSkippedOffset() > mStart.GetSkippedOffset());
       allowHyphenBreakBeforeNextChar = false;
     }
   }
 
@@ -8383,39 +8384,38 @@ nsTextFrame::AddInlineMinISizeForFlow(ns
       aData->OptionallyBreak();
     }
     aData->mCurrentLine += provider.GetFontMetrics()->EmHeight();
     aData->mTrailingWhitespace = 0;
     return;
   }
 
   AutoTArray<bool,BIG_TEXT_NODE_SIZE> hyphBuffer;
-  bool *hyphBreakBefore = nullptr;
   if (hyphenating) {
-    hyphBreakBefore = hyphBuffer.AppendElements(flowEndInTextRun - start,
-                                                fallible);
-    if (hyphBreakBefore) {
+    if (hyphBuffer.AppendElements(flowEndInTextRun - start, fallible)) {
       provider.GetHyphenationBreaks(Range(start, flowEndInTextRun),
-                                    hyphBreakBefore);
+                                    hyphBuffer.Elements());
+    } else {
+      hyphenating = false;
     }
   }
 
   for (uint32_t i = start, wordStart = start; i <= flowEndInTextRun; ++i) {
     bool preformattedNewline = false;
     bool preformattedTab = false;
     if (i < flowEndInTextRun) {
       // XXXldb Shouldn't we be including the newline as part of the
       // segment that it ends rather than part of the segment that it
       // starts?
       preformattedNewline = preformatNewlines && textRun->CharIsNewline(i);
       preformattedTab = preformatTabs && textRun->CharIsTab(i);
       if (!textRun->CanBreakLineBefore(i) &&
           !preformattedNewline &&
           !preformattedTab &&
-          (!hyphBreakBefore || !hyphBreakBefore[i - start]))
+          (!hyphenating || !hyphBuffer[i - start]))
       {
         // we can't break here (and it's not the end of the flow)
         continue;
       }
     }
 
     if (i > wordStart) {
       nscoord width = NSToCoordCeilClamped(
@@ -8452,18 +8452,18 @@ nsTextFrame::AddInlineMinISizeForFlow(ns
         AdvanceToNextTab(aData->mCurrentLine, this, textRun, tabWidth);
       aData->mCurrentLine = nscoord(afterTab + spacing.mAfter);
       wordStart = i + 1;
     } else if (i < flowEndInTextRun ||
         (i == textRun->GetLength() &&
          (textRun->GetFlags() & nsTextFrameUtils::TEXT_HAS_TRAILING_BREAK))) {
       if (preformattedNewline) {
         aData->ForceBreak();
-      } else if (i < flowEndInTextRun && hyphBreakBefore &&
-                 hyphBreakBefore[i - start]) {
+      } else if (i < flowEndInTextRun && hyphenating &&
+                 hyphBuffer[i - start]) {
         aData->OptionallyBreak(NSToCoordRound(provider.GetHyphenWidth()));
       } else {
         aData->OptionallyBreak();
       }
       wordStart = i;
     }
   }