diff --git a/js/src/ds/Fifo.h b/js/src/ds/Fifo.h
index cea46c12ac7a..84851ac947d8 100644
--- a/js/src/ds/Fifo.h
+++ b/js/src/ds/Fifo.h
@@ -46,11 +46,19 @@ class Fifo
 
   private:
     // Maintain invariants after adding or removing entries.
-    void fixup() {
-        if (front_.empty() && !rear_.empty()) {
-            front_.swap(rear_);
-            Reverse(front_.begin(), front_.end());
+    bool fixup() {
+        if (!front_.empty())
+            return true;
+
+        if (!front_.reserve(rear_.length()))
+            return false;
+
+        while (!rear_.empty()) {
+            front_.infallibleAppend(mozilla::Move(rear_.back()));
+            rear_.popBack();
         }
+
+        return true;
     }
 
   public:
@@ -90,7 +98,10 @@ class Fifo
     MOZ_MUST_USE bool pushBack(U&& u) {
         if (!rear_.append(mozilla::Forward<U>(u)))
             return false;
-        fixup();
+        if (!fixup()) {
+            rear_.popBack();
+            return false;
+        }
         return true;
     }
 
@@ -99,7 +110,10 @@ class Fifo
     MOZ_MUST_USE bool emplaceBack(Args&&... args) {
         if (!rear_.emplaceBack(mozilla::Forward<Args>(args)...))
             return false;
-        fixup();
+        if (!fixup()) {
+            rear_.popBack();
+            return false;
+        }
         return true;
     }
 
@@ -114,10 +128,20 @@ class Fifo
     }
 
     // Remove the front element from the queue.
-    void popFront() {
+    MOZ_MUST_USE bool popFront() {
         MOZ_ASSERT(!empty());
+        T t(mozilla::Move(front()));
         front_.popBack();
-        fixup();
+        if (!fixup()) {
+            // Attempt to remain in a valid state by reinserting the element
+            // back at the front. If we can't remain in a valid state in the
+            // face of OOMs, crash.
+            AutoEnterOOMUnsafeRegion oomUnsafe;
+            if (!front_.append(mozilla::Move(t)))
+                oomUnsafe.crash("js::Fifo::popFront");
+            return false;
+        }
+        return true;
     }
 
     // Clear all elements from the queue.
diff --git a/js/src/ds/TraceableFifo.h b/js/src/ds/TraceableFifo.h
index 67daad1fa7f5..95871688dc00 100644
--- a/js/src/ds/TraceableFifo.h
+++ b/js/src/ds/TraceableFifo.h
@@ -79,7 +79,7 @@ class MutableWrappedPtrOperations<TraceableFifo<T, Capacity, AllocPolicy>, Wrapp
         return fifo().emplaceBack(mozilla::Forward<Args...>(args...));
     }
 
-    void popFront() { fifo().popFront(); }
+    bool popFront() { return fifo().popFront(); }
     void clear() { fifo().clear(); }
 };
 
diff --git a/js/src/jsapi-tests/testGCExactRooting.cpp b/js/src/jsapi-tests/testGCExactRooting.cpp
index f4dc23dab474..38d2d8003c1c 100644
--- a/js/src/jsapi-tests/testGCExactRooting.cpp
+++ b/js/src/jsapi-tests/testGCExactRooting.cpp
@@ -323,7 +323,7 @@ BEGIN_TEST(testTraceableFifo)
         bool match;
         CHECK(JS_StringEqualsAscii(cx, JSID_TO_STRING(shapes.front()->propid()), buffer, &match));
         CHECK(match);
-        shapes.popFront();
+        CHECK(shapes.popFront());
     }
 
     CHECK(shapes.empty());
diff --git a/js/src/vm/Debugger.cpp b/js/src/vm/Debugger.cpp
index 2e8c4c9b2ce3..1cc59946ab3d 100644
--- a/js/src/vm/Debugger.cpp
+++ b/js/src/vm/Debugger.cpp
@@ -2298,7 +2298,10 @@ Debugger::appendAllocationSite(JSContext* cx, HandleObject obj, HandleSavedFrame
     }
 
     if (allocationsLog.length() > maxAllocationsLogLength) {
-        allocationsLog.popFront();
+        if (!allocationsLog.popFront()) {
+            ReportOutOfMemory(cx);
+            return false;
+        }
         MOZ_ASSERT(allocationsLog.length() == maxAllocationsLogLength);
         allocationsLogOverflowed = true;
     }
diff --git a/js/src/vm/DebuggerMemory.cpp b/js/src/vm/DebuggerMemory.cpp
index d7474c3aa25f..d48df08204b4 100644
--- a/js/src/vm/DebuggerMemory.cpp
+++ b/js/src/vm/DebuggerMemory.cpp
@@ -238,7 +238,10 @@ DebuggerMemory::drainAllocationsLog(JSContext* cx, unsigned argc, Value* vp)
         // Pop the front queue entry, and delete it immediately, so that the GC
         // sees the AllocationsLogEntry's HeapPtr barriers run atomically with
         // the change to the graph (the queue link).
-        dbg->allocationsLog.popFront();
+        if (!dbg->allocationsLog.popFront()) {
+            ReportOutOfMemory(cx);
+            return false;
+        }
     }
 
     dbg->allocationsLogOverflowed = false;
@@ -275,8 +278,12 @@ DebuggerMemory::setMaxAllocationsLogLength(JSContext* cx, unsigned argc, Value*
     Debugger* dbg = memory->getDebugger();
     dbg->maxAllocationsLogLength = max;
 
-    while (dbg->allocationsLog.length() > dbg->maxAllocationsLogLength)
-        dbg->allocationsLog.popFront();
+    while (dbg->allocationsLog.length() > dbg->maxAllocationsLogLength) {
+        if (!dbg->allocationsLog.popFront()) {
+            ReportOutOfMemory(cx);
+            return false;
+        }
+    }
 
     args.rval().setUndefined();
     return true;