diff --git a/mozilla/mailnews/imap/src/nsImapUtils.cpp b/mozilla/mailnews/imap/src/nsImapUtils.cpp
index 14003e8cd9b..555e7101db8 100644
--- a/mozilla/mailnews/imap/src/nsImapUtils.cpp
+++ b/mozilla/mailnews/imap/src/nsImapUtils.cpp
@@ -444,7 +444,7 @@ CreateUtf7ConvertedString(const char * aSourceString,
       // convert from 8 bit ascii string to modified utf7
       nsString unicodeStr(aSourceString);
       nsIUnicodeEncoder* encoder = nsnull;
-      aCharset.SetString("x-imap4-modified-utf7");
+      aCharset.Assign("x-imap4-modified-utf7");
       res = ccm->GetUnicodeEncoder(&aCharset, &encoder);
       if(NS_SUCCEEDED(res) && (nsnull != encoder)) 
       {
@@ -493,7 +493,7 @@ CreateUtf7ConvertedStringFromUnicode(const PRUnichar * aSourceString)
       // convert from 8 bit ascii string to modified utf7
       nsString unicodeStr(aSourceString);
       nsIUnicodeEncoder* encoder = nsnull;
-      aCharset.SetString("x-imap4-modified-utf7");
+      aCharset.Assign("x-imap4-modified-utf7");
       res = ccm->GetUnicodeEncoder(&aCharset, &encoder);
       if(NS_SUCCEEDED(res) && (nsnull != encoder)) 
       {
diff --git a/mozilla/mailnews/mime/emitters/src/nsMimeXULEmitter.cpp b/mozilla/mailnews/mime/emitters/src/nsMimeXULEmitter.cpp
index 16eb4858a38..af387321a64 100644
--- a/mozilla/mailnews/mime/emitters/src/nsMimeXULEmitter.cpp
+++ b/mozilla/mailnews/mime/emitters/src/nsMimeXULEmitter.cpp
@@ -483,12 +483,12 @@ nsMimeXULEmitter::DumpAddBookIcon(char *fromLine)
   char *newNameValue = nsEscape(name, url_XAlphas);
   if (newNameValue) 
   {
-    newName.SetString(newNameValue);
+    newName.Assign(newNameValue);
     PR_FREEIF(newNameValue);
   }
   else
   {
-    newName.SetString(name);
+    newName.Assign(name);
   }
 
   // Strip off extra quotes...
diff --git a/mozilla/mailnews/mime/src/comi18n.cpp b/mozilla/mailnews/mime/src/comi18n.cpp
index 828634318ad..06343b437c8 100644
--- a/mozilla/mailnews/mime/src/comi18n.cpp
+++ b/mozilla/mailnews/mime/src/comi18n.cpp
@@ -1243,13 +1243,13 @@ PRInt32 MimeCharsetConverterClass::Initialize(const char* from_charset, const ch
 
   NS_ASSERTION(NULL == mEncoder, "No reinitialization allowed.");
 
-  mInputCharset.SetString(from_charset);     // remember input charset for a hint
+  mInputCharset.Assign(from_charset);     // remember input charset for a hint
   if (mInputCharset.IsEmpty()) {
-    mInputCharset.SetString("ISO-8859-1");
+    mInputCharset.Assign("ISO-8859-1");
   }
-  mOutputCharset.SetString(to_charset);      // remember output charset
+  mOutputCharset.Assign(to_charset);      // remember output charset
   if (mOutputCharset.IsEmpty()) {
-    mOutputCharset.SetString("UTF-8");
+    mOutputCharset.Assign("UTF-8");
   }
   mAutoDetect = autoDetect;
   mMaxNumCharsDetect = maxNumCharsDetect;
@@ -1343,7 +1343,7 @@ PRInt32 MimeCharsetConverterClass::Convert(const char* inBuffer, const PRInt32 i
     nsDetectionConfident oConfident;
     res = mDetector->DoIt(inBuffer, inLength, &oCharset, oConfident);
     if (NS_SUCCEEDED(res) && (eBestAnswer == oConfident || eSureAnswer == oConfident)) {
-      aCharsetDetected.SetString(oCharset);
+      aCharsetDetected.Assign(oCharset);
 
       // Check if need a conversion.
       if (!NeedCharsetConversion(aCharsetDetected, mOutputCharset)) {