diff --git a/dom/base/WindowFeatures.cpp b/dom/base/WindowFeatures.cpp
deleted file mode 100644
index 0d1c3172f39f..000000000000
--- a/dom/base/WindowFeatures.cpp
+++ /dev/null
@@ -1,233 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#include "WindowFeatures.h"
-
-#include "nsINode.h"               // IsSpaceCharacter
-#include "nsContentUtils.h"        // nsContentUtils
-#include "nsDependentSubstring.h"  // Substring
-#include "nsReadableUtils.h"       // ToLowerCase
-
-#ifdef DEBUG
-/* static */
-bool WindowFeatures::IsLowerCase(const char* text) {
-  nsAutoCString before(text);
-  nsAutoCString after;
-  ToLowerCase(before, after);
-  return before == after;
-}
-#endif
-
-static bool IsFeatureSeparator(char aChar) {
-  // https://html.spec.whatwg.org/multipage/window-object.html#feature-separator
-  // A code point is a feature separator if it is ASCII whitespace, U+003D (=),
-  // or U+002C (,).
-  return IsSpaceCharacter(aChar) || aChar == '=' || aChar == ',';
-}
-
-template <class IterT, class CondT>
-void AdvanceWhile(IterT& aPosition, const IterT& aEnd, CondT aCondition) {
-  // https://infra.spec.whatwg.org/#collect-a-sequence-of-code-points
-  //
-  // Step 2. While `position` doesn’t point past the end of `input` and the
-  // code point at `position` within `input` meets the condition condition:
-  while (aCondition(*aPosition) && aPosition < aEnd) {
-    // Step 2.1. Append that code point to the end of `result`.
-    // (done by caller)
-
-    // Step 2.2. Advance `position` by 1.
-    ++aPosition;
-  }
-}
-
-template <class IterT, class CondT>
-nsTDependentSubstring<char> CollectSequence(IterT& aPosition, const IterT& aEnd,
-                                            CondT aCondition) {
-  // https://infra.spec.whatwg.org/#collect-a-sequence-of-code-points
-  // To collect a sequence of code points meeting a condition `condition` from
-  // a string `input`, given a position variable `position` tracking the
-  // position of the calling algorithm within `input`:
-
-  // Step 1. Let `result` be the empty string.
-  auto start = aPosition;
-
-  // Step 2.
-  AdvanceWhile(aPosition, aEnd, aCondition);
-
-  // Step 3. Return `result`.
-  return Substring(start, aPosition);
-}
-
-static void NormalizeName(nsAutoCString& aName) {
-  // https://html.spec.whatwg.org/multipage/window-object.html#normalizing-the-feature-name
-  if (aName == "screenx") {
-    aName = "left";
-  } else if (aName == "screeny") {
-    aName = "top";
-  } else if (aName == "innerwidth") {
-    aName = "width";
-  } else if (aName == "innerheight") {
-    aName = "height";
-  }
-}
-
-/* static */
-int32_t WindowFeatures::ParseIntegerWithFallback(const nsCString& aValue) {
-  // https://html.spec.whatwg.org/multipage/window-object.html#concept-window-open-features-parse-boolean
-  //
-  // Step 3. Let `parsed` be the result of parsing value as an integer.
-  nsContentUtils::ParseHTMLIntegerResultFlags parseResult;
-  int32_t parsed = nsContentUtils::ParseHTMLInteger(aValue, &parseResult);
-
-  // Step 4. If `parsed` is an error, then set it to 0.
-  //
-  // https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#rules-for-parsing-integers
-  //
-  // eParseHTMLInteger_NonStandard is not tested given:
-  //   * Step 4 allows leading whitespaces
-  //   * Step 6 allows a plus sign
-  //   * Step 8 does not disallow leading zeros
-  //   * Steps 6 and 9 allow `-0`
-  //
-  // eParseHTMLInteger_DidNotConsumeAllInput is not tested given:
-  //   * Step 8 collects digits and ignores remaining part
-  //
-  if (parseResult & nsContentUtils::eParseHTMLInteger_Error) {
-    parsed = 0;
-  }
-
-  return parsed;
-}
-
-/* static */
-bool WindowFeatures::ParseBool(const nsCString& aValue) {
-  // https://html.spec.whatwg.org/multipage/window-object.html#concept-window-open-features-parse-boolean
-  // To parse a boolean feature given a string `value`:
-
-  // Step 1. If `value` is the empty string, then return true.
-  if (aValue.IsEmpty()) {
-    return true;
-  }
-
-  // Step 2. If `value` is a case-sensitive match for "yes", then return true.
-  if (aValue == "yes") {
-    return true;
-  }
-
-  // Steps 3-4.
-  int32_t parsed = ParseIntegerWithFallback(aValue);
-
-  // Step 5. Return false if `parsed` is 0, and true otherwise.
-  return parsed != 0;
-}
-
-bool WindowFeatures::Tokenize(const nsACString& aFeatures) {
-  // https://html.spec.whatwg.org/multipage/window-object.html#concept-window-open-features-tokenize
-  // To tokenize the `features` argument:
-
-  // Step 1. Let `tokenizedFeatures` be a new ordered map.
-  // (implicit)
-
-  // Step 2. Let `position` point at the first code point of features.
-  auto position = aFeatures.BeginReading();
-
-  // Step 3. While `position` is not past the end of `features`:
-  auto end = aFeatures.EndReading();
-  while (position < end) {
-    // Step 3.1. Let `name` be the empty string.
-    // (implicit)
-
-    // Step 3.2. Let `value` be the empty string.
-    nsAutoCString value;
-
-    // Step 3.3. Collect a sequence of code points that are feature separators
-    // from `features` given `position`. This skips past leading separators
-    // before the name.
-    //
-    // NOTE: Do not collect given this value is unused.
-    AdvanceWhile(position, end, IsFeatureSeparator);
-
-    // Step 3.4. Collect a sequence of code points that are not feature
-    // separators from `features` given `position`. Set `name` to the collected
-    // characters, converted to ASCII lowercase.
-    nsAutoCString name(CollectSequence(
-        position, end, [](char c) { return !IsFeatureSeparator(c); }));
-    ToLowerCase(name);
-
-    // Step 3.5. Set `name` to the result of normalizing the feature name
-    // `name`.
-    NormalizeName(name);
-
-    // Step 3.6. While `position` is not past the end of `features` and the
-    // code point at `position` in features is not U+003D (=):
-    //
-    // Step 3.6.1. If the code point at `position` in features is U+002C (,),
-    // or if it is not a feature separator, then break.
-    //
-    // Step 3.6.2. Advance `position` by 1.
-    //
-    // NOTE: This skips to the first U+003D (=) but does not skip past a U+002C
-    //       (,) or a non-separator.
-    //
-    // The above means skip all whitespaces.
-    AdvanceWhile(position, end, [](char c) { return IsSpaceCharacter(c); });
-
-    // Step 3.7. If the code point at `position` in `features` is a feature
-    // separator:
-    if (position < end && IsFeatureSeparator(*position)) {
-      // Step 3.7.1. While `position` is not past the end of `features` and the
-      // code point at `position` in `features` is a feature separator:
-      //
-      // Step 3.7.1.1. If the code point at `position` in `features` is
-      // U+002C (,), then break.
-      //
-      // Step 3.7.1.2. Advance `position` by 1.
-      //
-      // NOTE: This skips to the first non-separator but does not skip past a
-      // U+002C (,).
-      AdvanceWhile(position, end,
-                   [](char c) { return IsFeatureSeparator(c) && c != ','; });
-
-      // Step 3.7.2. Collect a sequence of code points that are not feature
-      // separators code points from `features` given `position`. Set `value` to
-      // the collected code points, converted to ASCII lowercase.
-      value = CollectSequence(position, end,
-                              [](char c) { return !IsFeatureSeparator(c); });
-      ToLowerCase(value);
-    }
-
-    // Step 3.8. If `name` is not the empty string, then set
-    // `tokenizedFeatures[name]` to `value`.
-    if (!name.IsEmpty()) {
-      if (!tokenizedFeatures_.put(name, value)) {
-        return false;
-      }
-    }
-  }
-
-  // Step 4. Return `tokenizedFeatures`.
-  return true;
-}
-
-void WindowFeatures::Stringify(nsAutoCString& aOutput) {
-  MOZ_ASSERT(aOutput.IsEmpty());
-
-  for (auto r = tokenizedFeatures_.all(); !r.empty(); r.popFront()) {
-    if (!aOutput.IsEmpty()) {
-      aOutput.Append(',');
-    }
-
-    const nsCString& name = r.front().key();
-    const nsCString& value = r.front().value();
-
-    aOutput.Append(name);
-
-    if (!value.IsEmpty()) {
-      aOutput.Append('=');
-      aOutput.Append(value);
-    }
-  }
-}
diff --git a/dom/base/WindowFeatures.h b/dom/base/WindowFeatures.h
deleted file mode 100644
index 634533c9fe95..000000000000
--- a/dom/base/WindowFeatures.h
+++ /dev/null
@@ -1,131 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifndef mozilla_dom_WindowFeatures_h
-#define mozilla_dom_WindowFeatures_h
-
-#include "mozilla/Assertions.h"  // MOZ_ASSERT
-#include "mozilla/HashTable.h"   // mozilla::HashMap
-
-#include "nsStringFwd.h"  // nsCString, nsACString, nsAutoCString, nsLiteralCString
-#include "nsTStringHasher.h"  // mozilla::DefaultHasher<nsCString>
-
-namespace mozilla {
-namespace dom {
-
-// Represents `tokenizedFeatures` in
-// https://html.spec.whatwg.org/multipage/window-object.html#concept-window-open-features-tokenize
-// with accessor methods for values.
-class WindowFeatures {
- public:
-  WindowFeatures() = default;
-
-  WindowFeatures(const WindowFeatures& aOther) = delete;
-  WindowFeatures& operator=(const WindowFeatures& aOther) = delete;
-
-  WindowFeatures(WindowFeatures&& aOther) = delete;
-  WindowFeatures& operator=(WindowFeatures&& aOther) = delete;
-
-  // Tokenizes `aFeatures` and stores the result map in member field.
-  // This should be called at the begining, only once.
-  //
-  // Returns true if successfully tokenized, false otherwise.
-  bool Tokenize(const nsACString& aFeatures);
-
-  // Returns true if the `aName` feature is specified.
-  template <size_t N>
-  bool Exists(const char (&aName)[N]) const {
-    MOZ_ASSERT(IsLowerCase(aName));
-    nsLiteralCString name(aName);
-    return tokenizedFeatures_.has(name);
-  }
-
-  // Returns string value of `aName` feature.
-  // The feature must exist.
-  template <size_t N>
-  const nsCString& Get(const char (&aName)[N]) const {
-    MOZ_ASSERT(IsLowerCase(aName));
-    nsLiteralCString name(aName);
-    auto p = tokenizedFeatures_.lookup(name);
-    MOZ_ASSERT(p.found());
-
-    return p->value();
-  }
-
-  // Returns integer value of `aName` feature.
-  // The feature must exist.
-  template <size_t N>
-  int32_t GetInt(const char (&aName)[N]) const {
-    const nsCString& value = Get(aName);
-    return ParseIntegerWithFallback(value);
-  }
-
-  // Returns bool value of `aName` feature.
-  // The feature must exist.
-  template <size_t N>
-  bool GetBool(const char (&aName)[N]) const {
-    const nsCString& value = Get(aName);
-    return ParseBool(value);
-  }
-
-  // Returns bool value of `aName` feature.
-  // If the feature doesn't exist, returns `aDefault`.
-  //
-  // If `aPresenceFlag` is provided and the feature exists, it's set to `true`.
-  // (note that the value isn't overwritten if the feature doesn't exist)
-  template <size_t N>
-  bool GetBoolWithDefault(const char (&aName)[N], bool aDefault,
-                          bool* aPresenceFlag = nullptr) const {
-    MOZ_ASSERT(IsLowerCase(aName));
-    nsLiteralCString name(aName);
-    auto p = tokenizedFeatures_.lookup(name);
-    if (p.found()) {
-      if (aPresenceFlag) {
-        *aPresenceFlag = true;
-      }
-      return ParseBool(p->value());
-    }
-    return aDefault;
-  }
-
-  // Remove the feature from the map.
-  template <size_t N>
-  void Remove(const char (&aName)[N]) {
-    MOZ_ASSERT(IsLowerCase(aName));
-    nsLiteralCString name(aName);
-    tokenizedFeatures_.remove(name);
-  }
-
-  // Returns true if there was no feature specified, or all features are
-  // removed by `Remove`.
-  //
-  // Note that this can be true even if `aFeatures` parameter of `Tokenize`
-  // is not empty, in case it contains no feature with non-empty name.
-  bool IsEmpty() const { return tokenizedFeatures_.empty(); }
-
-  // Stringify the map into `aOutput`.
-  // The result can be parsed again with `Tokenize`.
-  void Stringify(nsAutoCString& aOutput);
-
- private:
-#ifdef DEBUG
-  // Returns true if `text` does not contain any character that gets modified by
-  // `ToLowerCase`.
-  static bool IsLowerCase(const char* text);
-#endif
-
-  static int32_t ParseIntegerWithFallback(const nsCString& aValue);
-  static bool ParseBool(const nsCString& aValue);
-
-  // A map from feature name to feature value.
-  // If value is not provided, it's empty string.
-  mozilla::HashMap<nsCString, nsCString> tokenizedFeatures_;
-};
-
-}  // namespace dom
-}  // namespace mozilla
-
-#endif  // #ifndef mozilla_dom_WindowFeatures_h
diff --git a/dom/base/moz.build b/dom/base/moz.build
index 1016f7db4496..0411561e121b 100644
--- a/dom/base/moz.build
+++ b/dom/base/moz.build
@@ -253,7 +253,6 @@ EXPORTS.mozilla.dom += [
     'UserActivation.h',
     'ViewportMetaData.h',
     'VisualViewport.h',
-    'WindowFeatures.h',
     'WindowOrientationObserver.h',
     'WindowProxyHolder.h',
 ]
@@ -426,7 +425,6 @@ UNIFIED_SOURCES += [
     'ViewportMetaData.cpp',
     'VisualViewport.cpp',
     'WindowDestroyedEvent.cpp',
-    'WindowFeatures.cpp',
     'WindowNamedPropertiesHandler.cpp',
     'WindowOrientationObserver.cpp',
     'XPathGenerator.cpp',
diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index d0b32b1e720d..2c8855b05706 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -1181,14 +1181,11 @@ nsContentUtils::InternalSerializeAutocompleteAttribute(
 }
 
 // Parse an integer according to HTML spec
-template <class StringT>
-int32_t nsContentUtils::ParseHTMLIntegerImpl(
-    const StringT& aValue, ParseHTMLIntegerResultFlags* aResult) {
-  using CharT = typename StringT::char_type;
-
+int32_t nsContentUtils::ParseHTMLInteger(const nsAString& aValue,
+                                         ParseHTMLIntegerResultFlags* aResult) {
   int result = eParseHTMLInteger_NoFlags;
 
-  typename StringT::const_iterator iter, end;
+  nsAString::const_iterator iter, end;
   aValue.BeginReading(iter);
   aValue.EndReading(end);
 
@@ -1204,11 +1201,11 @@ int32_t nsContentUtils::ParseHTMLIntegerImpl(
   }
 
   int sign = 1;
-  if (*iter == CharT('-')) {
+  if (*iter == char16_t('-')) {
     sign = -1;
     result |= eParseHTMLInteger_Negative;
     ++iter;
-  } else if (*iter == CharT('+')) {
+  } else if (*iter == char16_t('+')) {
     result |= eParseHTMLInteger_NonStandard;
     ++iter;
   }
@@ -1219,7 +1216,7 @@ int32_t nsContentUtils::ParseHTMLIntegerImpl(
   // Check for leading zeros first.
   uint64_t leadingZeros = 0;
   while (iter != end) {
-    if (*iter != CharT('0')) {
+    if (*iter != char16_t('0')) {
       break;
     }
 
@@ -1229,8 +1226,8 @@ int32_t nsContentUtils::ParseHTMLIntegerImpl(
   }
 
   while (iter != end) {
-    if (*iter >= CharT('0') && *iter <= CharT('9')) {
-      value = (value * 10) + (*iter - CharT('0')) * sign;
+    if (*iter >= char16_t('0') && *iter <= char16_t('9')) {
+      value = (value * 10) + (*iter - char16_t('0')) * sign;
       ++iter;
       if (!value.isValid()) {
         result |= eParseHTMLInteger_Error | eParseHTMLInteger_ErrorOverflow;
@@ -1260,17 +1257,6 @@ int32_t nsContentUtils::ParseHTMLIntegerImpl(
   return value.isValid() ? value.value() : 0;
 }
 
-// Parse an integer according to HTML spec
-int32_t nsContentUtils::ParseHTMLInteger(const nsAString& aValue,
-                                         ParseHTMLIntegerResultFlags* aResult) {
-  return ParseHTMLIntegerImpl(aValue, aResult);
-}
-
-int32_t nsContentUtils::ParseHTMLInteger(const nsACString& aValue,
-                                         ParseHTMLIntegerResultFlags* aResult) {
-  return ParseHTMLIntegerImpl(aValue, aResult);
-}
-
 #define SKIP_WHITESPACE(iter, end_iter, end_res)                 \
   while ((iter) != (end_iter) && nsCRT::IsAsciiSpace(*(iter))) { \
     ++(iter);                                                    \
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index ec0d74d66c58..285b0147d4eb 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -614,12 +614,7 @@ class nsContentUtils {
   enum ParseHTMLIntegerResultFlags {
     eParseHTMLInteger_NoFlags = 0,
     // eParseHTMLInteger_NonStandard is set if the string representation of the
-    // integer was not the canonical one, but matches at least one of the
-    // following:
-    //   * had leading whitespaces
-    //   * had '+' sign
-    //   * had leading '0'
-    //   * was '-0'
+    // integer was not the canonical one (e.g. had extra leading '+' or '0').
     eParseHTMLInteger_NonStandard = 1 << 0,
     eParseHTMLInteger_DidNotConsumeAllInput = 1 << 1,
     // Set if one or more error flags were set.
@@ -631,15 +626,7 @@ class nsContentUtils {
   };
   static int32_t ParseHTMLInteger(const nsAString& aValue,
                                   ParseHTMLIntegerResultFlags* aResult);
-  static int32_t ParseHTMLInteger(const nsACString& aValue,
-                                  ParseHTMLIntegerResultFlags* aResult);
 
- private:
-  template <class StringT>
-  static int32_t ParseHTMLIntegerImpl(const StringT& aValue,
-                                      ParseHTMLIntegerResultFlags* aResult);
-
- public:
   /**
    * Parse a margin string of format 'top, right, bottom, left' into
    * an nsIntMargin.
diff --git a/dom/base/nsGlobalWindowOuter.cpp b/dom/base/nsGlobalWindowOuter.cpp
index 99311b0b1d72..c160b600d288 100644
--- a/dom/base/nsGlobalWindowOuter.cpp
+++ b/dom/base/nsGlobalWindowOuter.cpp
@@ -41,7 +41,6 @@
 #include "mozilla/dom/TimeoutHandler.h"
 #include "mozilla/dom/TimeoutManager.h"
 #include "mozilla/dom/WindowContext.h"
-#include "mozilla/dom/WindowFeatures.h"  // WindowFeatures
 #include "mozilla/dom/WindowProxyHolder.h"
 #include "mozilla/IntegerPrintfMacros.h"
 #if defined(MOZ_WIDGET_ANDROID)
@@ -77,6 +76,7 @@
 #include "jsfriendapi.h"
 #include "js/PropertySpec.h"
 #include "js/Wrapper.h"
+#include "nsCharSeparatedTokenizer.h"
 #include "nsReadableUtils.h"
 #include "nsJSEnvironment.h"
 #include "mozilla/dom/ScriptSettings.h"
@@ -7019,32 +7019,34 @@ nsresult nsGlobalWindowOuter::OpenInternal(
 
   NS_ASSERTION(mDocShell, "Must have docshell here");
 
-  NS_ConvertUTF16toUTF8 optionsUtf8(aOptions);
-
-  WindowFeatures features;
-  if (!features.Tokenize(optionsUtf8)) {
-    return NS_ERROR_FAILURE;
-  }
-
+  nsAutoCString options;
   bool forceNoOpener = aForceNoOpener;
-  if (features.Exists("noopener")) {
-    forceNoOpener = features.GetBool("noopener");
-    features.Remove("noopener");
-  }
-
   bool forceNoReferrer = false;
-  if (features.Exists("noreferrer")) {
-    forceNoReferrer = features.GetBool("noreferrer");
-    if (forceNoReferrer) {
+  // Unlike other window flags, "noopener" comes from splitting on commas with
+  // HTML whitespace trimming...
+  nsCharSeparatedTokenizerTemplate<nsContentUtils::IsHTMLWhitespace> tok(
+      aOptions, ',');
+  while (tok.hasMoreTokens()) {
+    auto nextTok = tok.nextToken();
+    if (nextTok.EqualsLiteral("noopener")) {
+      forceNoOpener = true;
+      continue;
+    }
+    if (StaticPrefs::dom_window_open_noreferrer_enabled() &&
+        nextTok.LowerCaseEqualsLiteral("noreferrer")) {
+      forceNoReferrer = true;
       // noreferrer implies noopener
       forceNoOpener = true;
+      continue;
     }
-    features.Remove("noreferrer");
+    // Want to create a copy of the options without 'noopener' because having
+    // 'noopener' in the options affects other window features.
+    if (!options.IsEmpty()) {
+      options.Append(',');
+    }
+    AppendUTF16toUTF8(nextTok, options);
   }
 
-  nsAutoCString options;
-  features.Stringify(options);
-
   // If current's top-level browsing context's active document's
   // cross-origin-opener-policy is "same-origin" or "same-origin + COEP" then
   // if currentDoc's origin is not same origin with currentDoc's top-level
diff --git a/startupcache/StartupCache.h b/startupcache/StartupCache.h
index 73d0aed92d6e..153000a7330a 100644
--- a/startupcache/StartupCache.h
+++ b/startupcache/StartupCache.h
@@ -11,7 +11,6 @@
 #include "nsClassHashtable.h"
 #include "nsComponentManagerUtils.h"
 #include "nsTArray.h"
-#include "nsTStringHasher.h"  // mozilla::DefaultHasher<nsCString>
 #include "nsZipArchive.h"
 #include "nsITimer.h"
 #include "nsIMemoryReporter.h"
@@ -122,6 +121,19 @@ struct StartupCacheEntry {
   };
 };
 
+struct nsCStringHasher {
+  using Key = nsCString;
+  using Lookup = nsCString;
+
+  static HashNumber hash(const Lookup& aLookup) {
+    return HashString(aLookup.get());
+  }
+
+  static bool match(const Key& aKey, const Lookup& aLookup) {
+    return aKey.Equals(aLookup);
+  }
+};
+
 // We don't want to refcount StartupCache, and ObserverService wants to
 // refcount its listeners, so we'll let it refcount this instead.
 class StartupCacheListener final : public nsIObserver {
@@ -206,7 +218,7 @@ class StartupCache : public nsIMemoryReporter {
   static void ThreadedWrite(void* aClosure);
   static void ThreadedPrefetch(void* aClosure);
 
-  HashMap<nsCString, StartupCacheEntry> mTable;
+  HashMap<nsCString, StartupCacheEntry, nsCStringHasher> mTable;
   // owns references to the contents of tables which have been invalidated.
   // In theory grows forever if the cache is continually filled and then
   // invalidated, but this should not happen in practice.
diff --git a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-innerheight-innerwidth.html.ini b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-innerheight-innerwidth.html.ini
index 3445ae8c8eb6..dbf12eceab84 100644
--- a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-innerheight-innerwidth.html.ini
+++ b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-innerheight-innerwidth.html.ini
@@ -3,14 +3,10 @@
     if webrender and not debug: bug 1425588
     if (os == "android") and e10s: bug 1550895 (frequently fails on geckoview)
   ["innerwidth==401" should set width of opened window]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
+    expected: FAIL
 
   ["innerheight==402" should set height of opened window]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
+    expected: FAIL
 
   ["INNERHEIGHT=402" should set height of opened window]
     expected:
diff --git a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-noopener.html.ini b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-noopener.html.ini
index 1be9eb56b198..4930c51c2112 100644
--- a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-noopener.html.ini
+++ b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-noopener.html.ini
@@ -1,2 +1,20 @@
 [open-features-tokenization-noopener.html]
   disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1364696
+  [tokenization should skip window features separators before `name`]
+    expected: FAIL
+
+  [feature `name` should be converted to ASCII lowercase]
+    expected: FAIL
+
+  [after `name`, tokenization should skip window features separators that are not "=" or ","]
+    expected: FAIL
+
+  [Tokenizing should ignore window feature separators except "," after initial "=" and before value]
+    expected: FAIL
+
+  [Tokenizing should read characters until first window feature separator as `value`]
+    expected: FAIL
+
+  ["noopener" should be based on name (key), not value]
+    expected: FAIL
+
diff --git a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-noreferrer.html.ini b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-noreferrer.html.ini
index 7756183174fe..67a6ebaab506 100644
--- a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-noreferrer.html.ini
+++ b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-noreferrer.html.ini
@@ -1,3 +1,22 @@
 [open-features-tokenization-noreferrer.html]
   expected:
     if webrender and (os == "linux"): ["OK", "TIMEOUT", "CRASH"]
+
+  [Tokenizing "noreferrer" should ignore window feature separators except "," after initial "=" and before value]
+    expected: FAIL
+
+  [Tokenizing "noreferrer" should read characters until first window feature separator as `value`]
+    expected: FAIL
+
+  [After "noreferrer", tokenization should skip window features separators that are not "=" or ","]
+    expected: FAIL
+
+  [Integer values other than 0 should activate the feature]
+    expected: FAIL
+
+  [Tokenization of "noreferrer" should skip window features separators before feature]
+    expected: FAIL
+
+  [Feature "noreferrer" should be converted to ASCII lowercase]
+    expected: FAIL
+
diff --git a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-screenx-screeny.html.ini b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-screenx-screeny.html.ini
index bb38619bc8a6..f34745d53747 100644
--- a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-screenx-screeny.html.ini
+++ b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-screenx-screeny.html.ini
@@ -2,5 +2,69 @@
   disabled:
     if webrender and not debug: bug 1425588
     if verify and (os == "linux") and not debug: fails in verify mode
-    if os == "android": frequently hits timeout
+  ["screenx==141" should set left position of opened window]
+    expected: FAIL
+
+  ["screeny==142" should set top position of opened window]
+    expected: FAIL
+
+  ["screenx=141" should set left position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
+
+  ["screeny=142" should set top position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
+
+  ["\\nscreenx= 141" should set left position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
+
+  [" screeny = 142" should set top position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
+
+  ["screenX=141" should set left position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
+
+  [",screenx=141,," should set left position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
+
+  [",screeny=142,," should set top position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
+
+  ["screenY=142" should set top position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
+
+  [" screenx = 141" should set left position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
+
+  ["SCREENX=141" should set left position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
+
+  ["SCREENY=142" should set top position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
+
+  ["\\nscreeny= 142" should set top position of opened window]
+    expected:
+      if (os == "android") and not e10s: FAIL
+      if (os == "android") and e10s: FAIL
 
diff --git a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-top-left.html.ini b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-top-left.html.ini
index 98e6ebb3425a..25380f83e3a5 100644
--- a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-top-left.html.ini
+++ b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-top-left.html.ini
@@ -3,19 +3,13 @@
     if webrender and not debug: bug 1425588
     if verify and (os == "linux") and not debug: fails in verify mode
   ["left==141" should set left position of opened window]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
+    expected: FAIL
 
   ["top==142" should set top position of opened window]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
+    expected: FAIL
 
   ["top=152==left=152" should set top and left position of opened window]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
+    expected: FAIL
 
   [",left=141,," should set left position of opened window]
     expected:
diff --git a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-width-height.html.ini b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-width-height.html.ini
index 1d32c8c9897d..9385f41fa1c6 100644
--- a/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-width-height.html.ini
+++ b/testing/web-platform/meta/html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/open-features-tokenization-width-height.html.ini
@@ -3,27 +3,16 @@
     if webrender and not debug: bug 1425588
     if (os == "android") and e10s: bug 1550895 (frequently fails on geckoview)
   ["width==401" should set width of opened window]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
+    expected: FAIL
 
   ["height==402" should set height of opened window]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
-      if devedition and os == "win" and bits == 32: FAIL # bug 1540551
+    expected: FAIL
 
   ["height==402 width = 401" should set height and width of opened window]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
-      if devedition and os == "win" and bits == 32: FAIL # bug 1540551
+    expected: FAIL
 
   [",height=402,,width==401" should set height and width of opened window]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
-      if devedition and os == "win" and bits == 32: FAIL # bug 1540551
+    expected: FAIL
 
   ["\\nheight= 402" should set height of opened window]
     expected:
diff --git a/toolkit/components/telemetry/Histograms.json b/toolkit/components/telemetry/Histograms.json
index 55d0c87b13ff..796983490cc1 100644
--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -14949,16 +14949,6 @@
     "bug_numbers": [1597956, 1614905],
     "description": "milliseconds to complete a TLS session resumption with external cache"
   },
-  "WINDOW_OPEN_OUTER_SIZE": {
-    "record_in_processes": ["main", "content"],
-    "products": ["firefox"],
-    "alert_emails": ["tfujisawa.birchill@mozilla.com"],
-    "expires_in_version": "80",
-    "kind": "boolean",
-    "bug_numbers": [1624150],
-    "releaseChannelCollection": "opt-out",
-    "description": "Flag indicating consumer of non-standard outerWidth/outerHeight features in window.open"
-  },
   "WINDOW_REMOTE_SUBFRAMES_ENABLED_STATUS": {
     "record_in_processes": ["main"],
     "products": ["firefox"],
diff --git a/toolkit/components/windowwatcher/nsWindowWatcher.cpp b/toolkit/components/windowwatcher/nsWindowWatcher.cpp
index 4479a018c628..b6054a02b968 100644
--- a/toolkit/components/windowwatcher/nsWindowWatcher.cpp
+++ b/toolkit/components/windowwatcher/nsWindowWatcher.cpp
@@ -63,7 +63,6 @@
 #include "mozilla/ResultExtensions.h"
 #include "mozilla/StaticPrefs_fission.h"
 #include "mozilla/StaticPrefs_full_screen_api.h"
-#include "mozilla/Telemetry.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/Storage.h"
 #include "mozilla/dom/ScriptSettings.h"
@@ -318,7 +317,9 @@ struct SizeSpec {
         mOuterHeightSpecified(false),
         mInnerWidthSpecified(false),
         mInnerHeightSpecified(false),
-        mLockAspectRatio(false) {}
+        mLockAspectRatio(false),
+        mUseDefaultWidth(false),
+        mUseDefaultHeight(false) {}
 
   int32_t mLeft;
   int32_t mTop;
@@ -335,6 +336,11 @@ struct SizeSpec {
   bool mInnerHeightSpecified;
   bool mLockAspectRatio;
 
+  // If these booleans are true, don't look at the corresponding width values
+  // even if they're specified -- they'll be bogus
+  bool mUseDefaultWidth;
+  bool mUseDefaultHeight;
+
   bool PositionSpecified() const { return mLeftSpecified || mTopSpecified; }
 
   bool SizeSpecified() const { return WidthSpecified() || HeightSpecified(); }
@@ -405,7 +411,8 @@ static bool CheckUserContextCompatibility(nsIDocShell* aDocShell) {
   return subjectPrincipal->GetUserContextId() == userContextId;
 }
 
-nsresult nsWindowWatcher::CreateChromeWindow(nsIWebBrowserChrome* aParentChrome,
+nsresult nsWindowWatcher::CreateChromeWindow(const nsACString& aFeatures,
+                                             nsIWebBrowserChrome* aParentChrome,
                                              uint32_t aChromeFlags,
                                              nsIOpenWindowInfo* aOpenWindowInfo,
                                              nsIWebBrowserChrome** aResult) {
@@ -437,18 +444,21 @@ nsresult nsWindowWatcher::CreateChromeWindow(nsIWebBrowserChrome* aParentChrome,
  * the size.
  *
  * @param aFeatures
- *        The features that was used to open the window.
+ *        The features string that was used to open the window.
  * @param aTreeOwner
  *        The nsIDocShellTreeOwner of the newly opened window. If null,
  *        this function is a no-op.
  */
 void nsWindowWatcher::MaybeDisablePersistence(
-    const SizeSpec& sizeSpec, nsIDocShellTreeOwner* aTreeOwner) {
+    const nsACString& aFeatures, nsIDocShellTreeOwner* aTreeOwner) {
   if (!aTreeOwner) {
     return;
   }
 
-  if (sizeSpec.SizeSpecified()) {
+  // At the moment, the strings "height=" or "width=" never happen
+  // outside a size specification, so we can do this the Q&D way.
+  if (PL_strcasestr(aFeatures.BeginReading(), "width=") ||
+      PL_strcasestr(aFeatures.BeginReading(), "height=")) {
     aTreeOwner->SetPersistence(false, false, false);
   }
 }
@@ -513,13 +523,10 @@ nsWindowWatcher::OpenWindowWithRemoteTab(nsIRemoteTab* aRemoteTab,
     return NS_ERROR_UNEXPECTED;
   }
 
-  WindowFeatures features;
-  features.Tokenize(aFeatures);
-
   SizeSpec sizeSpec;
-  CalcSizeSpec(features, sizeSpec);
+  CalcSizeSpec(aFeatures, sizeSpec);
 
-  uint32_t chromeFlags = CalculateChromeFlagsForChild(features, sizeSpec);
+  uint32_t chromeFlags = CalculateChromeFlagsForChild(aFeatures, sizeSpec);
 
   if (isPrivateBrowsingWindow) {
     chromeFlags |= nsIWebBrowserChrome::CHROME_PRIVATE_WINDOW;
@@ -536,7 +543,7 @@ nsWindowWatcher::OpenWindowWithRemoteTab(nsIRemoteTab* aRemoteTab,
   nsCOMPtr<nsIWebBrowserChrome> parentChrome(do_GetInterface(parentTreeOwner));
   nsCOMPtr<nsIWebBrowserChrome> newWindowChrome;
 
-  CreateChromeWindow(parentChrome, chromeFlags, aOpenWindowInfo,
+  CreateChromeWindow(aFeatures, parentChrome, chromeFlags, aOpenWindowInfo,
                      getter_AddRefs(newWindowChrome));
 
   if (NS_WARN_IF(!newWindowChrome)) {
@@ -567,7 +574,7 @@ nsWindowWatcher::OpenWindowWithRemoteTab(nsIRemoteTab* aRemoteTab,
   // that will also run with out-of-process tabs.
   MOZ_ASSERT(chromeContext->UseRemoteTabs());
 
-  MaybeDisablePersistence(sizeSpec, chromeTreeOwner);
+  MaybeDisablePersistence(aFeatures, chromeTreeOwner);
 
   SizeOpenedWindow(chromeTreeOwner, parentWindowOuter, false, sizeSpec,
                    Some(aOpenerFullZoom));
@@ -599,6 +606,7 @@ nsresult nsWindowWatcher::OpenWindowInternal(
 
   uint32_t chromeFlags;
   nsAutoString name;           // string version of aName
+  nsAutoCString features;      // string version of aFeatures
   nsCOMPtr<nsIURI> uriToLoad;  // from aUrl, if any
   nsCOMPtr<nsIDocShellTreeOwner>
       parentTreeOwner;            // from the parent window, if any
@@ -636,13 +644,11 @@ nsresult nsWindowWatcher::OpenWindowInternal(
     name.SetIsVoid(true);
   }
 
-  WindowFeatures features;
-  nsAutoCString featuresStr;
   if (aFeatures) {
-    featuresStr.Assign(aFeatures);
-    features.Tokenize(featuresStr);
+    features.Assign(aFeatures);
+    features.StripWhitespace();
   } else {
-    featuresStr.SetIsVoid(true);
+    features.SetIsVoid(true);
   }
 
   RefPtr<BrowsingContext> parentBC(
@@ -685,13 +691,6 @@ nsresult nsWindowWatcher::OpenWindowInternal(
 
   bool isCallerChrome = nsContentUtils::LegacyIsCallerChromeOrNativeCode();
 
-  if (!hasChromeParent) {
-    bool outerSizeUsed =
-        features.Exists("outerwidth") || features.Exists("outerheight");
-    mozilla::Telemetry::Accumulate(mozilla::Telemetry::WINDOW_OPEN_OUTER_SIZE,
-                                   outerSizeUsed);
-  }
-
   SizeSpec sizeSpec;
   CalcSizeSpec(features, sizeSpec);
 
@@ -840,8 +839,8 @@ nsresult nsWindowWatcher::OpenWindowInternal(
       if (provider) {
         rv = provider->ProvideWindow(openWindowInfo, chromeFlags, aCalledFromJS,
                                      sizeSpec.WidthSpecified(), uriToLoad, name,
-                                     featuresStr, aForceNoOpener,
-                                     aForceNoReferrer, aLoadState, &windowIsNew,
+                                     features, aForceNoOpener, aForceNoReferrer,
+                                     aLoadState, &windowIsNew,
                                      getter_AddRefs(newBC));
 
         if (NS_SUCCEEDED(rv) && newBC) {
@@ -937,8 +936,9 @@ nsresult nsWindowWatcher::OpenWindowInternal(
          completely honest: we clear that indicator if the opener is chrome, so
          that the downstream consumer can treat the indicator to mean simply
          that the new window is subject to popup control. */
-      rv = CreateChromeWindow(parentChrome, chromeFlags, openWindowInfo,
-                              getter_AddRefs(newChrome));
+      rv = CreateChromeWindow(features, parentChrome, chromeFlags,
+                              openWindowInfo, getter_AddRefs(newChrome));
+
       if (parentTopInnerWindow) {
         parentTopInnerWindow->Resume();
       }
@@ -1031,7 +1031,7 @@ nsresult nsWindowWatcher::OpenWindowInternal(
   if (isNewToplevelWindow) {
     nsCOMPtr<nsIDocShellTreeOwner> newTreeOwner;
     newDocShell->GetTreeOwner(getter_AddRefs(newTreeOwner));
-    MaybeDisablePersistence(sizeSpec, newTreeOwner);
+    MaybeDisablePersistence(features, newTreeOwner);
   }
 
   if (aDialog && aArgv) {
@@ -1649,43 +1649,41 @@ nsresult nsWindowWatcher::URIfromURL(const char* aURL,
   return NS_NewURI(aURI, aURL, baseURI);
 }
 
+#define NS_CALCULATE_CHROME_FLAG_FOR(feature, flag) \
+  chromeFlags |=                                    \
+      WinHasOption(aFeatures, (feature), 0, &presenceFlag) ? (flag) : 0;
 // static
 uint32_t nsWindowWatcher::CalculateChromeFlagsHelper(
-    uint32_t aInitialFlags, const WindowFeatures& aFeatures,
-    const SizeSpec& aSizeSpec, bool* presenceFlag, bool aHasChromeParent) {
+    uint32_t aInitialFlags, const nsACString& aFeatures,
+    const SizeSpec& aSizeSpec, bool& presenceFlag, bool aHasChromeParent) {
   uint32_t chromeFlags = aInitialFlags;
 
-  if (aFeatures.GetBoolWithDefault("titlebar", false, presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_TITLEBAR;
-  }
-  if (aFeatures.GetBoolWithDefault("close", false, presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_WINDOW_CLOSE;
-  }
-  if (aFeatures.GetBoolWithDefault("toolbar", false, presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_TOOLBAR;
-  }
-  if (aFeatures.GetBoolWithDefault("location", false, presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_LOCATIONBAR;
-  }
-  if (aFeatures.GetBoolWithDefault("personalbar", false, presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_PERSONAL_TOOLBAR;
-  }
-  if (aFeatures.GetBoolWithDefault("status", false, presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_STATUSBAR;
-  }
-  if (aFeatures.GetBoolWithDefault("menubar", false, presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_MENUBAR;
-  }
-  if (aFeatures.GetBoolWithDefault("resizable", false, presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_WINDOW_RESIZE;
-  }
-  if (aFeatures.GetBoolWithDefault("minimizable", false, presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_WINDOW_MIN;
-  }
+  // NS_CALCULATE_CHROME_FLAG_FOR requires aFeatures, presenceFlag, and
+  // chromeFlags to be in scope.
 
-  if (aFeatures.GetBoolWithDefault("scrollbars", true, presenceFlag)) {
+  NS_CALCULATE_CHROME_FLAG_FOR("titlebar",
+                               nsIWebBrowserChrome::CHROME_TITLEBAR);
+  NS_CALCULATE_CHROME_FLAG_FOR("close",
+                               nsIWebBrowserChrome::CHROME_WINDOW_CLOSE);
+  NS_CALCULATE_CHROME_FLAG_FOR("toolbar", nsIWebBrowserChrome::CHROME_TOOLBAR);
+  NS_CALCULATE_CHROME_FLAG_FOR("location",
+                               nsIWebBrowserChrome::CHROME_LOCATIONBAR);
+  NS_CALCULATE_CHROME_FLAG_FOR("personalbar",
+                               nsIWebBrowserChrome::CHROME_PERSONAL_TOOLBAR);
+  NS_CALCULATE_CHROME_FLAG_FOR("status", nsIWebBrowserChrome::CHROME_STATUSBAR);
+  NS_CALCULATE_CHROME_FLAG_FOR("menubar", nsIWebBrowserChrome::CHROME_MENUBAR);
+  NS_CALCULATE_CHROME_FLAG_FOR("resizable",
+                               nsIWebBrowserChrome::CHROME_WINDOW_RESIZE);
+  NS_CALCULATE_CHROME_FLAG_FOR("minimizable",
+                               nsIWebBrowserChrome::CHROME_WINDOW_MIN);
+
+  // default scrollbar to "on," unless explicitly turned off
+  bool scrollbarsPresent = false;
+  if (WinHasOption(aFeatures, "scrollbars", 1, &scrollbarsPresent) ||
+      !scrollbarsPresent) {
     chromeFlags |= nsIWebBrowserChrome::CHROME_SCROLLBARS;
   }
+  presenceFlag = presenceFlag || scrollbarsPresent;
 
   if (aHasChromeParent) {
     return chromeFlags;
@@ -1741,32 +1739,37 @@ uint32_t nsWindowWatcher::EnsureFlagsSafeForContent(uint32_t aChromeFlags,
 }
 
 // static
-bool nsWindowWatcher::ShouldOpenPopup(const WindowFeatures& aFeatures,
+bool nsWindowWatcher::ShouldOpenPopup(const nsACString& aFeatures,
                                       const SizeSpec& aSizeSpec) {
-  if (aFeatures.IsEmpty()) {
+  if (aFeatures.IsVoid()) {
     return false;
   }
 
   // Follow Google Chrome's behavior that opens a popup depending on
   // the following features.
-  if (!aFeatures.GetBoolWithDefault("location", false) &&
-      !aFeatures.GetBoolWithDefault("toolbar", false)) {
+  bool unused;
+  if (!WinHasOption(aFeatures, "location", 0, &unused) &&
+      !WinHasOption(aFeatures, "toolbar", 0, &unused)) {
     return true;
   }
 
-  if (!aFeatures.GetBoolWithDefault("menubar", false)) {
+  if (!WinHasOption(aFeatures, "menubar", 0, &unused)) {
     return true;
   }
 
-  if (!aFeatures.GetBoolWithDefault("resizable", true)) {
+  // `resizable` defaults to true.
+  // Should open popup only when explicitly specified to 0.
+  bool resizablePresent = false;
+  if (!WinHasOption(aFeatures, "resizable", 0, &resizablePresent) &&
+      resizablePresent) {
     return true;
   }
 
-  if (!aFeatures.GetBoolWithDefault("scrollbars", false)) {
+  if (!WinHasOption(aFeatures, "scrollbars", 0, &unused)) {
     return true;
   }
 
-  if (!aFeatures.GetBoolWithDefault("status", false)) {
+  if (!WinHasOption(aFeatures, "status", 0, &unused)) {
     return true;
   }
 
@@ -1788,13 +1791,15 @@ bool nsWindowWatcher::ShouldOpenPopup(const WindowFeatures& aFeatures,
  */
 // static
 uint32_t nsWindowWatcher::CalculateChromeFlagsForChild(
-    const WindowFeatures& aFeatures, const SizeSpec& aSizeSpec) {
-  if (aFeatures.IsEmpty()) {
+    const nsACString& aFeatures, const SizeSpec& aSizeSpec) {
+  if (aFeatures.IsVoid()) {
     return nsIWebBrowserChrome::CHROME_ALL;
   }
 
-  uint32_t chromeFlags = CalculateChromeFlagsHelper(
-      nsIWebBrowserChrome::CHROME_WINDOW_BORDERS, aFeatures, aSizeSpec);
+  bool presenceFlag = false;
+  uint32_t chromeFlags =
+      CalculateChromeFlagsHelper(nsIWebBrowserChrome::CHROME_WINDOW_BORDERS,
+                                 aFeatures, aSizeSpec, presenceFlag);
 
   return EnsureFlagsSafeForContent(chromeFlags);
 }
@@ -1812,7 +1817,7 @@ uint32_t nsWindowWatcher::CalculateChromeFlagsForChild(
  */
 // static
 uint32_t nsWindowWatcher::CalculateChromeFlagsForParent(
-    mozIDOMWindowProxy* aParent, const WindowFeatures& aFeatures,
+    mozIDOMWindowProxy* aParent, const nsACString& aFeatures,
     const SizeSpec& aSizeSpec, bool aDialog, bool aChromeURL,
     bool aHasChromeParent, bool aCalledFromJS) {
   MOZ_ASSERT(XRE_IsParentProcess());
@@ -1822,7 +1827,7 @@ uint32_t nsWindowWatcher::CalculateChromeFlagsForParent(
 
   // The features string is made void by OpenWindowInternal
   // if nullptr was originally passed as the features string.
-  if (aFeatures.IsEmpty()) {
+  if (aFeatures.IsVoid()) {
     chromeFlags = nsIWebBrowserChrome::CHROME_ALL;
     if (aDialog) {
       chromeFlags |= nsIWebBrowserChrome::CHROME_OPENAS_DIALOG |
@@ -1841,29 +1846,29 @@ uint32_t nsWindowWatcher::CalculateChromeFlagsForParent(
      in the standards-compliant window.(normal)open. */
 
   bool presenceFlag = false;
-  if (aDialog && aFeatures.GetBoolWithDefault("all", false, &presenceFlag)) {
+  if (aDialog && WinHasOption(aFeatures, "all", 0, &presenceFlag)) {
     chromeFlags = nsIWebBrowserChrome::CHROME_ALL;
   }
 
   /* Next, allow explicitly named options to override the initial settings */
   chromeFlags = CalculateChromeFlagsHelper(chromeFlags, aFeatures, aSizeSpec,
-                                           &presenceFlag, aHasChromeParent);
+                                           presenceFlag, aHasChromeParent);
 
   // Determine whether the window is a private browsing window
-  if (aFeatures.GetBoolWithDefault("private", false, &presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_PRIVATE_WINDOW;
-  }
-  if (aFeatures.GetBoolWithDefault("non-private", false, &presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_NON_PRIVATE_WINDOW;
-  }
+  chromeFlags |= WinHasOption(aFeatures, "private", 0, &presenceFlag)
+                     ? nsIWebBrowserChrome::CHROME_PRIVATE_WINDOW
+                     : 0;
+  chromeFlags |= WinHasOption(aFeatures, "non-private", 0, &presenceFlag)
+                     ? nsIWebBrowserChrome::CHROME_NON_PRIVATE_WINDOW
+                     : 0;
 
   // Determine whether the window should have remote tabs.
   bool remote = BrowserTabsRemoteAutostart();
 
   if (remote) {
-    remote = !aFeatures.GetBoolWithDefault("non-remote", false, &presenceFlag);
+    remote = !WinHasOption(aFeatures, "non-remote", 0, &presenceFlag);
   } else {
-    remote = aFeatures.GetBoolWithDefault("remote", false, &presenceFlag);
+    remote = WinHasOption(aFeatures, "remote", 0, &presenceFlag);
   }
 
   if (remote) {
@@ -1874,19 +1879,18 @@ uint32_t nsWindowWatcher::CalculateChromeFlagsForParent(
   bool fission = StaticPrefs::fission_autostart();
 
   if (fission) {
-    fission =
-        !aFeatures.GetBoolWithDefault("non-fission", false, &presenceFlag);
+    fission = !WinHasOption(aFeatures, "non-fission", 0, &presenceFlag);
   } else {
-    fission = aFeatures.GetBoolWithDefault("fission", false, &presenceFlag);
+    fission = WinHasOption(aFeatures, "fission", 0, &presenceFlag);
   }
 
   if (fission) {
     chromeFlags |= nsIWebBrowserChrome::CHROME_FISSION_WINDOW;
   }
 
-  if (aFeatures.GetBoolWithDefault("popup", false, &presenceFlag)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_WINDOW_POPUP;
-  }
+  chromeFlags |= WinHasOption(aFeatures, "popup", 0, &presenceFlag)
+                     ? nsIWebBrowserChrome::CHROME_WINDOW_POPUP
+                     : 0;
 
   /* OK.
      Normal browser windows, in spite of a stated pattern of turning off
@@ -1897,15 +1901,15 @@ uint32_t nsWindowWatcher::CalculateChromeFlagsForParent(
 
   // default titlebar and closebox to "on," if not mentioned at all
   if (!(chromeFlags & nsIWebBrowserChrome::CHROME_WINDOW_POPUP)) {
-    if (!aFeatures.Exists("titlebar")) {
+    if (!PL_strcasestr(aFeatures.BeginReading(), "titlebar")) {
       chromeFlags |= nsIWebBrowserChrome::CHROME_TITLEBAR;
     }
-    if (!aFeatures.Exists("close")) {
+    if (!PL_strcasestr(aFeatures.BeginReading(), "close")) {
       chromeFlags |= nsIWebBrowserChrome::CHROME_WINDOW_CLOSE;
     }
   }
 
-  if (aDialog && !aFeatures.IsEmpty() && !presenceFlag) {
+  if (aDialog && !aFeatures.IsVoid() && !presenceFlag) {
     chromeFlags = nsIWebBrowserChrome::CHROME_DEFAULT;
   }
 
@@ -1913,35 +1917,35 @@ uint32_t nsWindowWatcher::CalculateChromeFlagsForParent(
      with the features that are more operating hints than appearance
      instructions. (Note modality implies dependence.) */
 
-  if (aFeatures.GetBoolWithDefault("alwayslowered", false) ||
-      aFeatures.GetBoolWithDefault("z-lock", false)) {
+  if (WinHasOption(aFeatures, "alwaysLowered", 0, nullptr) ||
+      WinHasOption(aFeatures, "z-lock", 0, nullptr)) {
     chromeFlags |= nsIWebBrowserChrome::CHROME_WINDOW_LOWERED;
-  } else if (aFeatures.GetBoolWithDefault("alwaysraised", false)) {
+  } else if (WinHasOption(aFeatures, "alwaysRaised", 0, nullptr)) {
     chromeFlags |= nsIWebBrowserChrome::CHROME_WINDOW_RAISED;
   }
 
-  if (aFeatures.GetBoolWithDefault("suppressanimation", false)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_SUPPRESS_ANIMATION;
-  }
-  if (aFeatures.GetBoolWithDefault("alwaysontop", false)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_ALWAYS_ON_TOP;
-  }
-  if (aFeatures.GetBoolWithDefault("chrome", false)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_OPENAS_CHROME;
-  }
-  if (aFeatures.GetBoolWithDefault("extrachrome", false)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_EXTRA;
-  }
-  if (aFeatures.GetBoolWithDefault("centerscreen", false)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_CENTER_SCREEN;
-  }
-  if (aFeatures.GetBoolWithDefault("dependent", false)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_DEPENDENT;
-  }
-  if (aFeatures.GetBoolWithDefault("modal", false)) {
-    chromeFlags |= nsIWebBrowserChrome::CHROME_MODAL |
-                   nsIWebBrowserChrome::CHROME_DEPENDENT;
-  }
+  chromeFlags |= WinHasOption(aFeatures, "suppressanimation", 0, nullptr)
+                     ? nsIWebBrowserChrome::CHROME_SUPPRESS_ANIMATION
+                     : 0;
+  chromeFlags |= WinHasOption(aFeatures, "alwaysontop", 0, nullptr)
+                     ? nsIWebBrowserChrome::CHROME_ALWAYS_ON_TOP
+                     : 0;
+  chromeFlags |= WinHasOption(aFeatures, "chrome", 0, nullptr)
+                     ? nsIWebBrowserChrome::CHROME_OPENAS_CHROME
+                     : 0;
+  chromeFlags |= WinHasOption(aFeatures, "extrachrome", 0, nullptr)
+                     ? nsIWebBrowserChrome::CHROME_EXTRA
+                     : 0;
+  chromeFlags |= WinHasOption(aFeatures, "centerscreen", 0, nullptr)
+                     ? nsIWebBrowserChrome::CHROME_CENTER_SCREEN
+                     : 0;
+  chromeFlags |= WinHasOption(aFeatures, "dependent", 0, nullptr)
+                     ? nsIWebBrowserChrome::CHROME_DEPENDENT
+                     : 0;
+  chromeFlags |= WinHasOption(aFeatures, "modal", 0, nullptr)
+                     ? (nsIWebBrowserChrome::CHROME_MODAL |
+                        nsIWebBrowserChrome::CHROME_DEPENDENT)
+                     : 0;
 
   /* On mobile we want to ignore the dialog window feature, since the mobile UI
      does not provide any affordance for dialog windows. This does not interfere
@@ -1953,18 +1957,18 @@ uint32_t nsWindowWatcher::CalculateChromeFlagsForParent(
                       &disableDialogFeature);
 
   if (!disableDialogFeature) {
-    if (aFeatures.GetBoolWithDefault("dialog", false)) {
-      chromeFlags |= nsIWebBrowserChrome::CHROME_OPENAS_DIALOG;
-    }
+    chromeFlags |= WinHasOption(aFeatures, "dialog", 0, nullptr)
+                       ? nsIWebBrowserChrome::CHROME_OPENAS_DIALOG
+                       : 0;
   }
 
   /* and dialogs need to have the last word. assume dialogs are dialogs,
      and opened as chrome, unless explicitly told otherwise. */
   if (aDialog) {
-    if (!aFeatures.Exists("dialog")) {
+    if (!PL_strcasestr(aFeatures.BeginReading(), "dialog")) {
       chromeFlags |= nsIWebBrowserChrome::CHROME_OPENAS_DIALOG;
     }
-    if (!aFeatures.Exists("chrome")) {
+    if (!PL_strcasestr(aFeatures.BeginReading(), "chrome")) {
       chromeFlags |= nsIWebBrowserChrome::CHROME_OPENAS_CHROME;
     }
   }
@@ -1988,6 +1992,63 @@ uint32_t nsWindowWatcher::CalculateChromeFlagsForParent(
   return chromeFlags;
 }
 
+// static
+int32_t nsWindowWatcher::WinHasOption(const nsACString& aOptions,
+                                      const char* aName, int32_t aDefault,
+                                      bool* aPresenceFlag) {
+  if (aOptions.IsEmpty()) {
+    return 0;
+  }
+
+  const char* options = aOptions.BeginReading();
+  char* comma;
+  char* equal;
+  int32_t found = 0;
+
+#ifdef DEBUG
+  NS_ASSERTION(nsAutoCString(aOptions).FindCharInSet(" \n\r\t") == kNotFound,
+               "There should be no whitespace in this string!");
+#endif
+
+  while (true) {
+    comma = PL_strchr(options, ',');
+    if (comma) {
+      *comma = '\0';
+    }
+    equal = PL_strchr(options, '=');
+    if (equal) {
+      *equal = '\0';
+    }
+    if (nsCRT::strcasecmp(options, aName) == 0) {
+      if (aPresenceFlag) {
+        *aPresenceFlag = true;
+      }
+      if (equal)
+        if (*(equal + 1) == '*') {
+          found = aDefault;
+        } else if (nsCRT::strcasecmp(equal + 1, "yes") == 0) {
+          found = 1;
+        } else {
+          found = atoi(equal + 1);
+        }
+      else {
+        found = 1;
+      }
+    }
+    if (equal) {
+      *equal = '=';
+    }
+    if (comma) {
+      *comma = ',';
+    }
+    if (found || !comma) {
+      break;
+    }
+    options = comma + 1;
+  }
+  return found;
+}
+
 already_AddRefed<BrowsingContext> nsWindowWatcher::GetBrowsingContextByName(
     const nsAString& aName, bool aForceNoOpener,
     BrowsingContext* aCurrentContext) {
@@ -2019,148 +2080,70 @@ already_AddRefed<BrowsingContext> nsWindowWatcher::GetBrowsingContextByName(
 }
 
 // static
-void nsWindowWatcher::CalcSizeSpec(const WindowFeatures& aFeatures,
+void nsWindowWatcher::CalcSizeSpec(const nsACString& aFeatures,
                                    SizeSpec& aResult) {
-  // https://drafts.csswg.org/cssom-view/#set-up-browsing-context-features
-  // To set up browsing context features for a browsing context `target` given
-  // a map `tokenizedFeatures`:
+  // Parse position spec, if any, from aFeatures
+  bool present;
+  int32_t temp;
 
-  // Step 1. Let `x` be null.
-  // (implicit)
-
-  // Step 2. Let `y` be null.
-  // (implicit)
-
-  // Step 3. Let `width` be null.
-  // (implicit)
-
-  // Step 4. Let `height` be null.
-  // (implicit)
-
-  // Step 5. If `tokenizedFeatures["left"]` exists:
-  if (aFeatures.Exists("left")) {
-    // Step 5.1. Set `x` to the result of invoking the rules for parsing
-    // integers on `tokenizedFeatures["left"]`.
-    //
-    // Step 5.2. If `x` is an error, set `x` to 0.
-    int32_t x = aFeatures.GetInt("left");
-
-    // Step 5.3. Optionally, clamp `x` in a user-agent-defined manner so that
-    // the window does not move outside the Web-exposed available screen area.
-    // (done later)
-
-    // Step 5.4. Optionally, move `target`’s window such that the window’s
-    // left edge is at the horizontal coordinate `x` relative to the left edge
-    // of the Web-exposed screen area, measured in CSS pixels of target.
-    // The positive axis is rightward.
-    aResult.mLeft = x;
-    aResult.mLeftSpecified = true;
+  present = false;
+  if ((temp = WinHasOption(aFeatures, "left", 0, &present)) || present) {
+    aResult.mLeft = temp;
+  } else if ((temp = WinHasOption(aFeatures, "screenX", 0, &present)) ||
+             present) {
+    aResult.mLeft = temp;
   }
+  aResult.mLeftSpecified = present;
 
-  // Step 6. If `tokenizedFeatures["top"]` exists:
-  if (aFeatures.Exists("top")) {
-    // Step 6.1. Set `y` to the result of invoking the rules for parsing
-    // integers on `tokenizedFeatures["top"]`.
-    //
-    // Step 6.2. If `y` is an error, set `y` to 0.
-    int32_t y = aFeatures.GetInt("top");
-
-    // Step 6.3. Optionally, clamp `y` in a user-agent-defined manner so that
-    // the window does not move outside the Web-exposed available screen area.
-    // (done later)
-
-    // Step 6.4. Optionally, move `target`’s window such that the window’s top
-    // edge is at the vertical coordinate `y` relative to the top edge of the
-    // Web-exposed screen area, measured in CSS pixels of target. The positive
-    // axis is downward.
-    aResult.mTop = y;
-    aResult.mTopSpecified = true;
+  present = false;
+  if ((temp = WinHasOption(aFeatures, "top", 0, &present)) || present) {
+    aResult.mTop = temp;
+  } else if ((temp = WinHasOption(aFeatures, "screenY", 0, &present)) ||
+             present) {
+    aResult.mTop = temp;
   }
+  aResult.mTopSpecified = present;
 
-  // Non-standard extension.
-  // See bug 1623826
-  if (aFeatures.Exists("outerwidth")) {
-    int32_t width = aFeatures.GetInt("outerwidth");
-    if (width) {
-      aResult.mOuterWidth = width;
-      aResult.mOuterWidthSpecified = true;
+  // Parse size spec, if any. Chrome size overrides content size.
+  if ((temp = WinHasOption(aFeatures, "outerWidth", INT32_MIN, nullptr))) {
+    if (temp == INT32_MIN) {
+      aResult.mUseDefaultWidth = true;
+    } else {
+      aResult.mOuterWidth = temp;
     }
-  }
-
-  if (!aResult.mOuterWidthSpecified) {
-    // Step 7. If `tokenizedFeatures["width"]` exists:
-    if (aFeatures.Exists("width")) {
-      // Step 7.1. Set `width` to the result of invoking the rules for parsing
-      // integers on `tokenizedFeatures["width"]`.
-      //
-      // Step 7.2. If `width` is an error, set `width` to 0.
-      int32_t width = aFeatures.GetInt("width");
-
-      // Step 7.3. If `width` is not 0:
-      if (width) {
-        // Step 7.3.1. Optionally, clamp `width` in a user-agent-defined manner
-        // so that the window does not get too small or bigger than the
-        // Web-exposed available screen area.
-        // (done later)
-
-        // Step 7.3.2. Optionally, size `target`’s window by moving its right
-        // edge such that the distance between the left and right edges of the
-        // viewport are `width` CSS pixels of target.
-        aResult.mInnerWidth = width;
-        aResult.mInnerWidthSpecified = true;
-
-        // Step 7.3.3. Optionally, move target’s window in a user-agent-defined
-        // manner so that it does not grow outside the Web-exposed available
-        // screen area.
-        // (done later)
-      }
+    aResult.mOuterWidthSpecified = true;
+  } else if ((temp = WinHasOption(aFeatures, "width", INT32_MIN, nullptr)) ||
+             (temp =
+                  WinHasOption(aFeatures, "innerWidth", INT32_MIN, nullptr))) {
+    if (temp == INT32_MIN) {
+      aResult.mUseDefaultWidth = true;
+    } else {
+      aResult.mInnerWidth = temp;
     }
+    aResult.mInnerWidthSpecified = true;
   }
 
-  // Non-standard extension.
-  // See bug 1623826
-  if (aFeatures.Exists("outerheight")) {
-    int32_t height = aFeatures.GetInt("outerheight");
-    if (height) {
-      aResult.mOuterHeight = height;
-      aResult.mOuterHeightSpecified = true;
+  if ((temp = WinHasOption(aFeatures, "outerHeight", INT32_MIN, nullptr))) {
+    if (temp == INT32_MIN) {
+      aResult.mUseDefaultHeight = true;
+    } else {
+      aResult.mOuterHeight = temp;
     }
-  }
-
-  if (!aResult.mOuterHeightSpecified) {
-    // Step 8. If `tokenizedFeatures["height"]` exists:
-    if (aFeatures.Exists("height")) {
-      // Step 8.1. Set `height` to the result of invoking the rules for parsing
-      // integers on `tokenizedFeatures["height"]`.
-      //
-      // Step 8.2. If `height` is an error, set `height` to 0.
-      int32_t height = aFeatures.GetInt("height");
-
-      // Step 8.3. If `height` is not 0:
-      if (height) {
-        // Step 8.3.1. Optionally, clamp `height` in a user-agent-defined manner
-        // so that the window does not get too small or bigger than the
-        // Web-exposed available screen area.
-        // (done later)
-
-        // Step 8.3.2. Optionally, size `target`’s window by moving its bottom
-        // edge such that the distance between the top and bottom edges of the
-        // viewport are `height` CSS pixels of target.
-        aResult.mInnerHeight = height;
-        aResult.mInnerHeightSpecified = true;
-
-        // Step 8.3.3. Optionally, move target’s window in a user-agent-defined
-        // manner so that it does not grow outside the Web-exposed available
-        // screen area.
-        // (done later)
-      }
+    aResult.mOuterHeightSpecified = true;
+  } else if ((temp = WinHasOption(aFeatures, "height", INT32_MIN, nullptr)) ||
+             (temp =
+                  WinHasOption(aFeatures, "innerHeight", INT32_MIN, nullptr))) {
+    if (temp == INT32_MIN) {
+      aResult.mUseDefaultHeight = true;
+    } else {
+      aResult.mInnerHeight = temp;
     }
+    aResult.mInnerHeightSpecified = true;
   }
 
-  // NOTE: The value is handled only on chrome-priv code.
-  // See nsWindowWatcher::SizeOpenedWindow.
-  aResult.mLockAspectRatio =
-      aFeatures.GetBoolWithDefault("lockaspectratio", false);
+  if (WinHasOption(aFeatures, "lockaspectratio", 0, nullptr)) {
+    aResult.mLockAspectRatio = true;
+  }
 }
 
 /* Size and position a new window according to aSizeSpec. This method
@@ -2250,18 +2233,30 @@ void nsWindowWatcher::SizeOpenedWindow(nsIDocShellTreeOwner* aTreeOwner,
 
   // Set up width
   if (aSizeSpec.mOuterWidthSpecified) {
-    width = NSToIntRound(aSizeSpec.mOuterWidth * openerZoom);
+    if (!aSizeSpec.mUseDefaultWidth) {
+      width = NSToIntRound(aSizeSpec.mOuterWidth * openerZoom);
+    }  // Else specified to default; just use our existing width
   } else if (aSizeSpec.mInnerWidthSpecified) {
     sizeChromeWidth = false;
-    width = NSToIntRound(aSizeSpec.mInnerWidth * openerZoom);
+    if (aSizeSpec.mUseDefaultWidth) {
+      width = width - chromeWidth;
+    } else {
+      width = NSToIntRound(aSizeSpec.mInnerWidth * openerZoom);
+    }
   }
 
   // Set up height
   if (aSizeSpec.mOuterHeightSpecified) {
-    height = NSToIntRound(aSizeSpec.mOuterHeight * openerZoom);
+    if (!aSizeSpec.mUseDefaultHeight) {
+      height = NSToIntRound(aSizeSpec.mOuterHeight * openerZoom);
+    }  // Else specified to default; just use our existing height
   } else if (aSizeSpec.mInnerHeightSpecified) {
     sizeChromeHeight = false;
-    height = NSToIntRound(aSizeSpec.mInnerHeight * openerZoom);
+    if (aSizeSpec.mUseDefaultHeight) {
+      height = height - chromeHeight;
+    } else {
+      height = NSToIntRound(aSizeSpec.mInnerHeight * openerZoom);
+    }
   }
 
   bool positionSpecified = aSizeSpec.PositionSpecified();
diff --git a/toolkit/components/windowwatcher/nsWindowWatcher.h b/toolkit/components/windowwatcher/nsWindowWatcher.h
index ce864f014310..44d5237df1d1 100644
--- a/toolkit/components/windowwatcher/nsWindowWatcher.h
+++ b/toolkit/components/windowwatcher/nsWindowWatcher.h
@@ -25,7 +25,6 @@
 #include "nsIRemoteTab.h"
 #include "nsPIWindowWatcher.h"
 #include "nsTArray.h"
-#include "mozilla/dom/WindowFeatures.h"  // mozilla::dom::WindowFeatures
 
 class nsIURI;
 class nsIDocShellTreeItem;
@@ -87,20 +86,23 @@ class nsWindowWatcher : public nsIWindowWatcher,
   static nsresult URIfromURL(const char* aURL, mozIDOMWindowProxy* aParent,
                              nsIURI** aURI);
 
-  static bool ShouldOpenPopup(const mozilla::dom::WindowFeatures& aFeatures,
+  static bool ShouldOpenPopup(const nsACString& aFeatures,
                               const SizeSpec& aSizeSpec);
 
-  static uint32_t CalculateChromeFlagsForChild(
-      const mozilla::dom::WindowFeatures& aFeatures, const SizeSpec& aSizeSpec);
+  static uint32_t CalculateChromeFlagsForChild(const nsACString& aFeaturesStr,
+                                               const SizeSpec& aSizeSpec);
 
-  static uint32_t CalculateChromeFlagsForParent(
-      mozIDOMWindowProxy* aParent,
-      const mozilla::dom::WindowFeatures& aFeatures, const SizeSpec& aSizeSpec,
-      bool aDialog, bool aChromeURL, bool aHasChromeParent, bool aCalledFromJS);
+  static uint32_t CalculateChromeFlagsForParent(mozIDOMWindowProxy* aParent,
+                                                const nsACString& aFeaturesStr,
+                                                const SizeSpec& aSizeSpec,
+                                                bool aDialog, bool aChromeURL,
+                                                bool aHasChromeParent,
+                                                bool aCalledFromJS);
 
+  static int32_t WinHasOption(const nsACString& aOptions, const char* aName,
+                              int32_t aDefault, bool* aPresenceFlag);
   /* Compute the right SizeSpec based on aFeatures */
-  static void CalcSizeSpec(const mozilla::dom::WindowFeatures& aFeatures,
-                           SizeSpec& aResult);
+  static void CalcSizeSpec(const nsACString& aFeatures, SizeSpec& aResult);
   static void SizeOpenedWindow(
       nsIDocShellTreeOwner* aTreeOwner, mozIDOMWindowProxy* aParent,
       bool aIsCallerChrome, const SizeSpec& aSizeSpec,
@@ -111,18 +113,20 @@ class nsWindowWatcher : public nsIWindowWatcher,
                                  nsIDocShellTreeOwner** aResult);
 
  private:
-  nsresult CreateChromeWindow(nsIWebBrowserChrome* aParentChrome,
+  nsresult CreateChromeWindow(const nsACString& aFeatures,
+                              nsIWebBrowserChrome* aParentChrome,
                               uint32_t aChromeFlags,
                               nsIOpenWindowInfo* aOpenWindowInfo,
                               nsIWebBrowserChrome** aResult);
 
-  void MaybeDisablePersistence(const SizeSpec& sizeSpec,
+  void MaybeDisablePersistence(const nsACString& aFeatures,
                                nsIDocShellTreeOwner* aTreeOwner);
 
-  static uint32_t CalculateChromeFlagsHelper(
-      uint32_t aInitialFlags, const mozilla::dom::WindowFeatures& aFeatures,
-      const SizeSpec& aSizeSpec, bool* presenceFlag = nullptr,
-      bool aHasChromeParent = false);
+  static uint32_t CalculateChromeFlagsHelper(uint32_t aInitialFlags,
+                                             const nsACString& aFeatures,
+                                             const SizeSpec& aSizeSpec,
+                                             bool& presenceFlag,
+                                             bool aHasChromeParent = false);
   static uint32_t EnsureFlagsSafeForContent(uint32_t aChromeFlags,
                                             bool aChromeURL = false);
 
diff --git a/xpcom/string/moz.build b/xpcom/string/moz.build
index 3b0e44803492..c8da7234c1cc 100644
--- a/xpcom/string/moz.build
+++ b/xpcom/string/moz.build
@@ -28,7 +28,6 @@ EXPORTS += [
     'nsTLiteralString.h',
     'nsTPromiseFlatString.h',
     'nsTString.h',
-    'nsTStringHasher.h',
     'nsTStringRepr.h',
     'nsTSubstring.h',
     'nsTSubstringTuple.h',
diff --git a/xpcom/string/nsTStringHasher.h b/xpcom/string/nsTStringHasher.h
deleted file mode 100644
index 7b3f42ba5883..000000000000
--- a/xpcom/string/nsTStringHasher.h
+++ /dev/null
@@ -1,30 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifndef nsTStringHasher_h___
-#define nsTStringHasher_h___
-
-#include "mozilla/HashTable.h"  // mozilla::{DefaultHasher, HashNumber, HashString}
-
-namespace mozilla {
-
-template <typename T>
-struct DefaultHasher<nsTString<T>> {
-  using Key = nsTString<T>;
-  using Lookup = nsTString<T>;
-
-  static mozilla::HashNumber hash(const Lookup& aLookup) {
-    return mozilla::HashString(aLookup.get());
-  }
-
-  static bool match(const Key& aKey, const Lookup& aLookup) {
-    return aKey.Equals(aLookup);
-  }
-};
-
-}  // namespace mozilla
-
-#endif  // !defined(nsTStringHasher_h___)