diff --git a/string/obsolete/nsString.cpp b/string/obsolete/nsString.cpp
index ad9461f4b8ca..dbe9a38e181f 100644
--- a/string/obsolete/nsString.cpp
+++ b/string/obsolete/nsString.cpp
@@ -889,14 +889,14 @@ nsCString& nsCString::Assign(char aChar) {
  * @param 
  * @return
  */
-#ifdef AIX
+#if defined(AIX) || defined(XP_OS2_VACPP)
 nsCString& nsCString::operator=(const nsSubsumeCStr& aSubsumeString) {
-  nsSubsumeCStr temp(aSubsumeString);  // a temp is needed for the AIX compiler
+  nsSubsumeCStr temp(aSubsumeString);  // a temp is needed for the AIX and VAC++ compiler
   CSubsume(*this,temp);
 #else
 nsCString& nsCString::operator=(nsSubsumeCStr& aSubsumeString) {
   CSubsume(*this,aSubsumeString);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
   return *this;
 }
 #endif
@@ -1946,14 +1946,14 @@ nsCAutoString::nsCAutoString(PRUnichar aChar) : nsCString(){
  * @update  gess 1/4/99
  * @param   reference to a subsumeString
  */
-#ifdef AIX
+#if defined(AIX) || defined(XP_OS2_VACPP)
 nsCAutoString::nsCAutoString(const nsSubsumeCStr& aSubsumeStr) :nsCString() {
-  nsSubsumeCStr temp(aSubsumeStr);  // a temp is needed for the AIX compiler
+  nsSubsumeCStr temp(aSubsumeStr);  // a temp is needed for the AIX and VAC++ compilers
   CSubsume(*this,temp);
 #else
 nsCAutoString::nsCAutoString( nsSubsumeCStr& aSubsumeStr) :nsCString() {
   CSubsume(*this,aSubsumeStr);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
 }
 
 /**
diff --git a/string/obsolete/nsString.h b/string/obsolete/nsString.h
index 6c01c9205a57..e75cba6f42b5 100644
--- a/string/obsolete/nsString.h
+++ b/string/obsolete/nsString.h
@@ -237,6 +237,7 @@ public:
   nsSubsumeCStr operator+(char aChar);
 #endif
 
+
   /**********************************************************************
     Lexomorphic transforms...
    *********************************************************************/
@@ -432,8 +433,8 @@ public:
 
     // Yes, I know this makes assignment from a |nsSubsumeString| not do the special thing
     //  |nsSubsumeString| needs to go away
-  #ifdef AIX
-  nsCString& operator=(const nsSubsumeCStr& aSubsumeString);  // AIX requires a const here
+  #if defined(AIX) || defined(XP_OS2_VACPP)
+  nsCString& operator=(const nsSubsumeCStr& aSubsumeString);  // AIX and VAC++ requires a const here
   #else
   nsCString& operator=(nsSubsumeCStr& aSubsumeString);
   #endif
@@ -813,11 +814,11 @@ public:
 //  nsCAutoString(PRUnichar aChar);
 #endif
 
-#ifdef AIX
-    nsCAutoString(const nsSubsumeCStr& aSubsumeStr);  // AIX requires a const
+#if defined(AIX) || defined(XP_OS2_VACPP)
+    nsCAutoString(const nsSubsumeCStr& aSubsumeStr);  // AIX and VAC++ require a const
 #else
     nsCAutoString(nsSubsumeCStr& aSubsumeStr);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
 
 
 #ifndef NEW_STRING_APIS
diff --git a/string/obsolete/nsString2.h b/string/obsolete/nsString2.h
index fc71b6ed2eaf..b861f65b2077 100644
--- a/string/obsolete/nsString2.h
+++ b/string/obsolete/nsString2.h
@@ -124,8 +124,8 @@ public:
    * This constructor takes a subsumestr
    * @param   reference to subsumestr
    */
-#ifdef AIX
-  nsString(const nsSubsumeStr& aSubsumeStr);   // AIX requires a const here
+#if defined(AIX) || defined(XP_OS2_VACPP)
+  nsString(const nsSubsumeStr& aSubsumeStr);   // AIX and VAC++ require a const here
 #else
   nsString(nsSubsumeStr& aSubsumeStr);   
 #endif
@@ -468,8 +468,8 @@ public:
 
     // Yes, I know this makes assignment from a |nsSubsumeString| not do the special thing
     //  |nsSubsumeString| needs to go away
-  #ifdef AIX
-  nsString& operator=(const nsSubsumeStr& aSubsumeString);  // AIX requires a const here
+  #if defined(AIX) || defined(XP_OS2_VACPP)
+  nsString& operator=(const nsSubsumeStr& aSubsumeString);  // AIX and VAC++ requires a const here
   #else
   nsString& operator=(nsSubsumeStr& aSubsumeString);
   #endif
@@ -904,11 +904,11 @@ public:
 //  nsAutoString(const nsStr& aString);
 #endif
 
-#ifdef AIX
-    nsAutoString(const nsSubsumeStr& aSubsumeStr);  // AIX requires a const
+#if defined(AIX) || defined(XP_OS2_VACPP)
+    nsAutoString(const nsSubsumeStr& aSubsumeStr);  // AIX and VAC++ requires a const
 #else
     nsAutoString(nsSubsumeStr& aSubsumeStr);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
 
 
 #ifndef NEW_STRING_APIS
diff --git a/xpcom/ds/nsString.cpp b/xpcom/ds/nsString.cpp
index ad9461f4b8ca..dbe9a38e181f 100644
--- a/xpcom/ds/nsString.cpp
+++ b/xpcom/ds/nsString.cpp
@@ -889,14 +889,14 @@ nsCString& nsCString::Assign(char aChar) {
  * @param 
  * @return
  */
-#ifdef AIX
+#if defined(AIX) || defined(XP_OS2_VACPP)
 nsCString& nsCString::operator=(const nsSubsumeCStr& aSubsumeString) {
-  nsSubsumeCStr temp(aSubsumeString);  // a temp is needed for the AIX compiler
+  nsSubsumeCStr temp(aSubsumeString);  // a temp is needed for the AIX and VAC++ compiler
   CSubsume(*this,temp);
 #else
 nsCString& nsCString::operator=(nsSubsumeCStr& aSubsumeString) {
   CSubsume(*this,aSubsumeString);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
   return *this;
 }
 #endif
@@ -1946,14 +1946,14 @@ nsCAutoString::nsCAutoString(PRUnichar aChar) : nsCString(){
  * @update  gess 1/4/99
  * @param   reference to a subsumeString
  */
-#ifdef AIX
+#if defined(AIX) || defined(XP_OS2_VACPP)
 nsCAutoString::nsCAutoString(const nsSubsumeCStr& aSubsumeStr) :nsCString() {
-  nsSubsumeCStr temp(aSubsumeStr);  // a temp is needed for the AIX compiler
+  nsSubsumeCStr temp(aSubsumeStr);  // a temp is needed for the AIX and VAC++ compilers
   CSubsume(*this,temp);
 #else
 nsCAutoString::nsCAutoString( nsSubsumeCStr& aSubsumeStr) :nsCString() {
   CSubsume(*this,aSubsumeStr);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
 }
 
 /**
diff --git a/xpcom/ds/nsString.h b/xpcom/ds/nsString.h
index 6c01c9205a57..e75cba6f42b5 100644
--- a/xpcom/ds/nsString.h
+++ b/xpcom/ds/nsString.h
@@ -237,6 +237,7 @@ public:
   nsSubsumeCStr operator+(char aChar);
 #endif
 
+
   /**********************************************************************
     Lexomorphic transforms...
    *********************************************************************/
@@ -432,8 +433,8 @@ public:
 
     // Yes, I know this makes assignment from a |nsSubsumeString| not do the special thing
     //  |nsSubsumeString| needs to go away
-  #ifdef AIX
-  nsCString& operator=(const nsSubsumeCStr& aSubsumeString);  // AIX requires a const here
+  #if defined(AIX) || defined(XP_OS2_VACPP)
+  nsCString& operator=(const nsSubsumeCStr& aSubsumeString);  // AIX and VAC++ requires a const here
   #else
   nsCString& operator=(nsSubsumeCStr& aSubsumeString);
   #endif
@@ -813,11 +814,11 @@ public:
 //  nsCAutoString(PRUnichar aChar);
 #endif
 
-#ifdef AIX
-    nsCAutoString(const nsSubsumeCStr& aSubsumeStr);  // AIX requires a const
+#if defined(AIX) || defined(XP_OS2_VACPP)
+    nsCAutoString(const nsSubsumeCStr& aSubsumeStr);  // AIX and VAC++ require a const
 #else
     nsCAutoString(nsSubsumeCStr& aSubsumeStr);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
 
 
 #ifndef NEW_STRING_APIS
diff --git a/xpcom/ds/nsString2.h b/xpcom/ds/nsString2.h
index fc71b6ed2eaf..b861f65b2077 100644
--- a/xpcom/ds/nsString2.h
+++ b/xpcom/ds/nsString2.h
@@ -124,8 +124,8 @@ public:
    * This constructor takes a subsumestr
    * @param   reference to subsumestr
    */
-#ifdef AIX
-  nsString(const nsSubsumeStr& aSubsumeStr);   // AIX requires a const here
+#if defined(AIX) || defined(XP_OS2_VACPP)
+  nsString(const nsSubsumeStr& aSubsumeStr);   // AIX and VAC++ require a const here
 #else
   nsString(nsSubsumeStr& aSubsumeStr);   
 #endif
@@ -468,8 +468,8 @@ public:
 
     // Yes, I know this makes assignment from a |nsSubsumeString| not do the special thing
     //  |nsSubsumeString| needs to go away
-  #ifdef AIX
-  nsString& operator=(const nsSubsumeStr& aSubsumeString);  // AIX requires a const here
+  #if defined(AIX) || defined(XP_OS2_VACPP)
+  nsString& operator=(const nsSubsumeStr& aSubsumeString);  // AIX and VAC++ requires a const here
   #else
   nsString& operator=(nsSubsumeStr& aSubsumeString);
   #endif
@@ -904,11 +904,11 @@ public:
 //  nsAutoString(const nsStr& aString);
 #endif
 
-#ifdef AIX
-    nsAutoString(const nsSubsumeStr& aSubsumeStr);  // AIX requires a const
+#if defined(AIX) || defined(XP_OS2_VACPP)
+    nsAutoString(const nsSubsumeStr& aSubsumeStr);  // AIX and VAC++ requires a const
 #else
     nsAutoString(nsSubsumeStr& aSubsumeStr);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
 
 
 #ifndef NEW_STRING_APIS
diff --git a/xpcom/io/nsDirectoryService.cpp b/xpcom/io/nsDirectoryService.cpp
index e673ac84b3c2..193bf931cbbd 100644
--- a/xpcom/io/nsDirectoryService.cpp
+++ b/xpcom/io/nsDirectoryService.cpp
@@ -31,6 +31,8 @@
 #include <Files.h>
 #include <Memory.h>
 #include <Processes.h>
+#elif defined(XP_OS2)
+#define MAX_PATH _MAX_PATH
 #elif defined(XP_PC)
 #include <windows.h>
 #include <shlobj.h>
@@ -99,6 +101,17 @@ static nsresult GetCurrentProcessDirectory(nsILocalFile** aFile)
 
 
 #ifdef XP_PC
+#ifdef XP_OS2
+    PPIB ppib;
+    PTIB ptib;
+    char buffer[CCHMAXPATH];
+    DosGetInfoBlocks( &ptib, &ppib);
+    DosQueryModuleName( ppib->pib_hmte, CCHMAXPATH, buffer);
+    *strrchr( buffer, '\\') = '\0'; // XXX DBCS misery
+    localFile->InitWithPath(buffer);
+    *aFile = localFile;
+    return NS_OK;
+#else
     char buf[MAX_PATH];
     if ( ::GetModuleFileName(0, buf, sizeof(buf)) ) {
         // chop of the executable name by finding the rightmost backslash
@@ -110,6 +123,7 @@ static nsresult GetCurrentProcessDirectory(nsILocalFile** aFile)
         *aFile = localFile;
         return NS_OK;
     }
+#endif
 
 #elif defined(XP_MAC)
     // get info for the the current process to determine the directory
diff --git a/xpcom/io/nsFileSpec.cpp b/xpcom/io/nsFileSpec.cpp
index e76210435b3f..3d16ec9e2cb9 100644
--- a/xpcom/io/nsFileSpec.cpp
+++ b/xpcom/io/nsFileSpec.cpp
@@ -41,7 +41,7 @@
 #include <string.h>
 #include <stdio.h>
 
-#ifdef	XP_PC
+#if defined(XP_PC) && !defined(XP_OS2)
 #include <mbstring.h>
 #endif
 
@@ -357,7 +357,7 @@ char* nsSimpleCharString::GetLeaf(char inSeparator) const
         return nsnull;
 
     char* chars = mData->mString;
-#ifdef	XP_PC
+#if defined(XP_PC) && !defined(XP_OS2)
     const char* lastSeparator = (const char*) _mbsrchr((const unsigned char *) chars, inSeparator);
 #else
     const char* lastSeparator = strrchr(chars, inSeparator);
@@ -374,7 +374,7 @@ char* nsSimpleCharString::GetLeaf(char inSeparator) const
 
     // So now, separator was the last character. Poke in a null instead.
     *(char*)lastSeparator = '\0'; // Should use const_cast, but Unix has old compiler.
-#ifdef XP_PC
+#if defined(XP_PC) && !defined(XP_OS2)
     leafPointer = (const char*) _mbsrchr((const unsigned char *) chars, inSeparator);
 #else
     leafPointer = strrchr(chars, inSeparator);
diff --git a/xpcom/string/obsolete/nsString.cpp b/xpcom/string/obsolete/nsString.cpp
index ad9461f4b8ca..dbe9a38e181f 100644
--- a/xpcom/string/obsolete/nsString.cpp
+++ b/xpcom/string/obsolete/nsString.cpp
@@ -889,14 +889,14 @@ nsCString& nsCString::Assign(char aChar) {
  * @param 
  * @return
  */
-#ifdef AIX
+#if defined(AIX) || defined(XP_OS2_VACPP)
 nsCString& nsCString::operator=(const nsSubsumeCStr& aSubsumeString) {
-  nsSubsumeCStr temp(aSubsumeString);  // a temp is needed for the AIX compiler
+  nsSubsumeCStr temp(aSubsumeString);  // a temp is needed for the AIX and VAC++ compiler
   CSubsume(*this,temp);
 #else
 nsCString& nsCString::operator=(nsSubsumeCStr& aSubsumeString) {
   CSubsume(*this,aSubsumeString);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
   return *this;
 }
 #endif
@@ -1946,14 +1946,14 @@ nsCAutoString::nsCAutoString(PRUnichar aChar) : nsCString(){
  * @update  gess 1/4/99
  * @param   reference to a subsumeString
  */
-#ifdef AIX
+#if defined(AIX) || defined(XP_OS2_VACPP)
 nsCAutoString::nsCAutoString(const nsSubsumeCStr& aSubsumeStr) :nsCString() {
-  nsSubsumeCStr temp(aSubsumeStr);  // a temp is needed for the AIX compiler
+  nsSubsumeCStr temp(aSubsumeStr);  // a temp is needed for the AIX and VAC++ compilers
   CSubsume(*this,temp);
 #else
 nsCAutoString::nsCAutoString( nsSubsumeCStr& aSubsumeStr) :nsCString() {
   CSubsume(*this,aSubsumeStr);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
 }
 
 /**
diff --git a/xpcom/string/obsolete/nsString.h b/xpcom/string/obsolete/nsString.h
index 6c01c9205a57..e75cba6f42b5 100644
--- a/xpcom/string/obsolete/nsString.h
+++ b/xpcom/string/obsolete/nsString.h
@@ -237,6 +237,7 @@ public:
   nsSubsumeCStr operator+(char aChar);
 #endif
 
+
   /**********************************************************************
     Lexomorphic transforms...
    *********************************************************************/
@@ -432,8 +433,8 @@ public:
 
     // Yes, I know this makes assignment from a |nsSubsumeString| not do the special thing
     //  |nsSubsumeString| needs to go away
-  #ifdef AIX
-  nsCString& operator=(const nsSubsumeCStr& aSubsumeString);  // AIX requires a const here
+  #if defined(AIX) || defined(XP_OS2_VACPP)
+  nsCString& operator=(const nsSubsumeCStr& aSubsumeString);  // AIX and VAC++ requires a const here
   #else
   nsCString& operator=(nsSubsumeCStr& aSubsumeString);
   #endif
@@ -813,11 +814,11 @@ public:
 //  nsCAutoString(PRUnichar aChar);
 #endif
 
-#ifdef AIX
-    nsCAutoString(const nsSubsumeCStr& aSubsumeStr);  // AIX requires a const
+#if defined(AIX) || defined(XP_OS2_VACPP)
+    nsCAutoString(const nsSubsumeCStr& aSubsumeStr);  // AIX and VAC++ require a const
 #else
     nsCAutoString(nsSubsumeCStr& aSubsumeStr);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
 
 
 #ifndef NEW_STRING_APIS
diff --git a/xpcom/string/obsolete/nsString2.h b/xpcom/string/obsolete/nsString2.h
index fc71b6ed2eaf..b861f65b2077 100644
--- a/xpcom/string/obsolete/nsString2.h
+++ b/xpcom/string/obsolete/nsString2.h
@@ -124,8 +124,8 @@ public:
    * This constructor takes a subsumestr
    * @param   reference to subsumestr
    */
-#ifdef AIX
-  nsString(const nsSubsumeStr& aSubsumeStr);   // AIX requires a const here
+#if defined(AIX) || defined(XP_OS2_VACPP)
+  nsString(const nsSubsumeStr& aSubsumeStr);   // AIX and VAC++ require a const here
 #else
   nsString(nsSubsumeStr& aSubsumeStr);   
 #endif
@@ -468,8 +468,8 @@ public:
 
     // Yes, I know this makes assignment from a |nsSubsumeString| not do the special thing
     //  |nsSubsumeString| needs to go away
-  #ifdef AIX
-  nsString& operator=(const nsSubsumeStr& aSubsumeString);  // AIX requires a const here
+  #if defined(AIX) || defined(XP_OS2_VACPP)
+  nsString& operator=(const nsSubsumeStr& aSubsumeString);  // AIX and VAC++ requires a const here
   #else
   nsString& operator=(nsSubsumeStr& aSubsumeString);
   #endif
@@ -904,11 +904,11 @@ public:
 //  nsAutoString(const nsStr& aString);
 #endif
 
-#ifdef AIX
-    nsAutoString(const nsSubsumeStr& aSubsumeStr);  // AIX requires a const
+#if defined(AIX) || defined(XP_OS2_VACPP)
+    nsAutoString(const nsSubsumeStr& aSubsumeStr);  // AIX and VAC++ requires a const
 #else
     nsAutoString(nsSubsumeStr& aSubsumeStr);
-#endif // AIX
+#endif // AIX || XP_OS2_VACPP
 
 
 #ifndef NEW_STRING_APIS