--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -1282,17 +1282,17 @@ static already_AddRefed<mozilla::dom::No
 nsIDocument::nsIDocument()
   : nsINode(nullNodeInfo),
     mReferrerPolicySet(false),
     mReferrerPolicy(mozilla::net::RP_Unset),
     mBlockAllMixedContent(false),
     mBlockAllMixedContentPreloads(false),
     mUpgradeInsecureRequests(false),
     mUpgradeInsecurePreloads(false),
-    mCharacterSet(NS_LITERAL_CSTRING("ISO-8859-1")),
+    mCharacterSet(NS_LITERAL_CSTRING("windows-1252")),
     mCharacterSetSource(0),
     mParentDocument(nullptr),
     mCachedRootElement(nullptr),
     mNodeInfoManager(nullptr),
     mBidiEnabled(false),
     mMathMLEnabled(false),
     mIsInitialDocumentInWindow(false),
     mIgnoreDocGroupMismatches(false),

--- a/dom/html/MediaDocument.cpp
+++ b/dom/html/MediaDocument.cpp
@@ -288,17 +288,17 @@ MediaDocument::GetFileName(nsAString& aR
 
   nsAutoCString fileName;
   url->GetFileName(fileName);
   if (fileName.IsEmpty())
     return;
 
   nsAutoCString docCharset;
   // Now that the charset is set in |StartDocumentLoad| to the charset of
-  // the document viewer instead of a bogus value ("ISO-8859-1" set in
+  // the document viewer instead of a bogus value ("windows-1252" set in
   // |nsDocument|'s ctor), the priority is given to the current charset. 
   // This is necessary to deal with a media document being opened in a new 
   // window or a new tab, in which case |originCharset| of |nsIURI| is not 
   // reliable.
   if (mCharacterSetSource != kCharsetUninitialized) {  
     docCharset = mCharacterSet;
   } else {  
     // resort to |originCharset|

--- a/dom/jsurl/nsJSProtocolHandler.cpp
+++ b/dom/jsurl/nsJSProtocolHandler.cpp
@@ -287,22 +287,22 @@ nsresult nsJSThunk::EvaluateScript(nsICh
                    "How did we get a non-undefined return value?");
         nsAutoJSString result;
         if (!result.init(cx, v)) {
             return NS_ERROR_OUT_OF_MEMORY;
         }
 
         char *bytes;
         uint32_t bytesLen;
-        NS_NAMED_LITERAL_CSTRING(isoCharset, "ISO-8859-1");
+        NS_NAMED_LITERAL_CSTRING(isoCharset, "windows-1252");
         NS_NAMED_LITERAL_CSTRING(utf8Charset, "UTF-8");
         const nsLiteralCString *charset;
         if (IsISO88591(result)) {
             // For compatibility, if the result is ISO-8859-1, we use
-            // ISO-8859-1, so that people can compatibly create images
+            // windows-1252, so that people can compatibly create images
             // using javascript: URLs.
             bytes = ToNewCString(result);
             bytesLen = result.Length();
             charset = &isoCharset;
         }
         else {
             bytes = ToNewUTF8String(result, &bytesLen);
             charset = &utf8Charset;

--- a/editor/libeditor/TextEditor.cpp
+++ b/editor/libeditor/TextEditor.cpp
@@ -1325,17 +1325,17 @@ TextEditor::OutputToString(const nsAStri
     // This case will get triggered by password fields.
     aOutputString.Assign(*(ruleInfo.outString));
     return rv;
   }
 
   nsAutoCString charsetStr;
   rv = GetDocumentCharacterSet(charsetStr);
   if (NS_FAILED(rv) || charsetStr.IsEmpty()) {
-    charsetStr.AssignLiteral("ISO-8859-1");
+    charsetStr.AssignLiteral("windows-1252");
   }
 
   nsCOMPtr<nsIDocumentEncoder> encoder =
     GetAndInitDocEncoder(aFormatType, aFlags, charsetStr);
   if (NS_WARN_IF(!encoder)) {
     return NS_ERROR_FAILURE;
   }
 

--- a/parser/htmlparser/nsParser.cpp
+++ b/parser/htmlparser/nsParser.cpp
@@ -147,17 +147,17 @@ nsParser::Initialize(bool aConstructor)
   else {
     // nsCOMPtrs
     mObserver = nullptr;
     mUnusedInput.Truncate();
   }
 
   mContinueEvent = nullptr;
   mCharsetSource = kCharsetUninitialized;
-  mCharset.AssignLiteral("ISO-8859-1");
+  mCharset.AssignLiteral("windows-1252");
   mInternalState = NS_OK;
   mStreamStatus = NS_OK;
   mCommand = eViewNormal;
   mBlocked = 0;
   mFlags = NS_PARSER_FLAG_OBSERVERS_ENABLED |
            NS_PARSER_FLAG_CAN_TOKENIZE;
 
   mProcessingNetworkData = false;

--- a/toolkit/components/search/nsSearchService.js
+++ b/toolkit/components/search/nsSearchService.js
@@ -107,17 +107,18 @@ const CACHE_FILENAME = "search.json.mozl
 
 const NEW_LINES = /(\r\n|\r|\n)/;
 
 // Set an arbitrary cap on the maximum icon size. Without this, large icons can
 // cause big delays when loading them at startup.
 const MAX_ICON_SIZE   = 10000;
 
 // Default charset to use for sending search parameters. ISO-8859-1 is used to
-// match previous nsInternetSearchService behavior.
+// match previous nsInternetSearchService behavior as a URL parameter. Label
+// resolution causes windows-1252 to be actually used.
 const DEFAULT_QUERY_CHARSET = "ISO-8859-1";
 
 const SEARCH_BUNDLE = "chrome://global/locale/search/search.properties";
 const BRAND_BUNDLE = "chrome://branding/locale/brand.properties";
 
 const OPENSEARCH_NS_10  = "http://a9.com/-/spec/opensearch/1.0/";
 const OPENSEARCH_NS_11  = "http://a9.com/-/spec/opensearch/1.1/";
 

--- a/xpfe/components/directory/nsDirectoryViewer.cpp
+++ b/xpfe/components/directory/nsDirectoryViewer.cpp
@@ -546,18 +546,18 @@ nsHTTPIndex::~nsHTTPIndex()
 
 
 
 nsresult
 nsHTTPIndex::CommonInit()
 {
     nsresult	rv = NS_OK;
 
-    // set initial/default encoding to ISO-8859-1 (not UTF-8)
-    mEncoding = "ISO-8859-1";
+    // set initial/default encoding to windows-1252 (not UTF-8)
+    mEncoding = "windows-1252";
 
     mDirRDF = do_GetService(kRDFServiceCID, &rv);
     NS_ASSERTION(NS_SUCCEEDED(rv), "unable to get RDF service");
     if (NS_FAILED(rv)) {
       return(rv);
     }
 
     mInner = do_CreateInstance("@mozilla.org/rdf/datasource;1?name=in-memory-datasource", &rv);
@@ -598,18 +598,18 @@ nsHTTPIndex::CommonInit()
 }
 
 
 nsresult
 nsHTTPIndex::Init()
 {
 	nsresult	rv;
 
-	// set initial/default encoding to ISO-8859-1 (not UTF-8)
-	mEncoding = "ISO-8859-1";
+	// set initial/default encoding to windows-1252 (not UTF-8)
+	mEncoding = "windows-1252";
 
 	rv = CommonInit();
 	if (NS_FAILED(rv))	return(rv);
 
 	// (do this last) register this as a named data source with the RDF service
 	rv = mDirRDF->RegisterDataSource(this, false);
 	if (NS_FAILED(rv)) return(rv);