--- a/layout/style/nsStyleSet.cpp
+++ b/layout/style/nsStyleSet.cpp
@@ -1315,17 +1315,20 @@ nsStyleSet::ResolvePseudoElementStyle(El
     WalkRestrictionRule(aType, &ruleWalker);
     FileRules(EnumRulesMatching<PseudoElementRuleProcessorData>, &data,
               aParentElement, &ruleWalker);
     visitedRuleNode = ruleWalker.CurrentNode();
   }
 
   // For pseudos, |data.IsLink()| being true means that
   // our parent node is a link.
-  uint32_t flags = eNoFlags;
+  // Also: Flex containers shouldn't have pseudo-elements, so given that we're
+  // looking up pseudo-element style, make sure we're not treating our node as
+  // a flex item.
+  uint32_t flags = eSkipFlexItemStyleFixup;
   if (aType == nsCSSPseudoElements::ePseudo_before ||
       aType == nsCSSPseudoElements::ePseudo_after) {
     flags |= eDoAnimation;
   }
 
   return GetContext(aParentContext, ruleNode, visitedRuleNode,
                     nsCSSPseudoElements::GetPseudoAtom(aType), aType,
                     aParentElement, flags);
@@ -1378,17 +1381,20 @@ nsStyleSet::ProbePseudoElementStyle(Elem
     WalkRestrictionRule(aType, &ruleWalker);
     FileRules(EnumRulesMatching<PseudoElementRuleProcessorData>, &data,
               aParentElement, &ruleWalker);
     visitedRuleNode = ruleWalker.CurrentNode();
   }
 
   // For pseudos, |data.IsLink()| being true means that
   // our parent node is a link.
-  uint32_t flags = eNoFlags;
+  // Also: Flex containers shouldn't have pseudo-elements, so given that we're
+  // looking up pseudo-element style, make sure we're not treating our node as
+  // a flex item.
+  uint32_t flags = eSkipFlexItemStyleFixup;
   if (aType == nsCSSPseudoElements::ePseudo_before ||
       aType == nsCSSPseudoElements::ePseudo_after) {
     flags |= eDoAnimation;
   }
 
   nsRefPtr<nsStyleContext> result =
     GetContext(aParentContext, ruleNode, visitedRuleNode,
                pseudoTag, aType,