Please set "javascript.options.jit.content" to false in greprefs\all.js case you
get crashes at startup! (Then it would also be helpful to know your system
configuration; please post it in the mozilla.dev.ports.os2 newsgroup.)

This build of SeaMonkey for OS/2 was made from code in comm-central and
mozilla-1.9.1 dated 2009-02-08 06:57:57 PST (changesets 1873:5ccc635e5a2a and
23255:c8099a4c91c3, resp.).
But the build could only be completed (with GCC 3.3.5) by adding the patches for
bug 451278 and bug 453705.
See all patches against mozilla-1.9.1 below.

diff --git a/js/src/xpconnect/src/qsgen.py b/js/src/xpconnect/src/qsgen.py
--- a/js/src/xpconnect/src/qsgen.py
+++ b/js/src/xpconnect/src/qsgen.py
@@ -470,6 +470,12 @@
                 "XPCVariant::newVariant(ccx, ${argVal})));\n"
                 "    if (!${name})\n"
                 "        return JS_FALSE;\n")
+            if os.name == 'os2': # Workaround for GCC 3.3.x bug.
+                template = (
+                    "    nsCOMPtr<nsIVariant> ${name}("
+                    "XPCVariant::newVariant(ccx, ${argVal}));\n"
+                    "    if (!${name})\n"
+                    "        return JS_FALSE;\n")
             f.write(substitute(template, params))
             return
         elif type.name == 'nsIAtom':
diff --git a/xpcom/string/public/nsTString.h b/xpcom/string/public/nsTString.h
--- a/xpcom/string/public/nsTString.h
+++ b/xpcom/string/public/nsTString.h
@@ -439,19 +439,24 @@ class nsTFixedString_CharT : public nsTS
          *        fixed-size buffer to be used by the string (the contents of
          *        this buffer may be modified by the string)
          * @param storageSize
          *        the size of the fixed buffer
          * @param length (optional)
          *        the length of the string already contained in the buffer
          */

+#ifdef XP_OS2 /* Workaround for GCC 3.3.x bug. */
+      nsTFixedString_CharT( char_type* data, size_type storageSize ) NS_COM;
+      nsTFixedString_CharT( char_type* data, size_type storageSize, size_type length ) NS_COM;
+#else
       NS_COM nsTFixedString_CharT( char_type* data, size_type storageSize );

       NS_COM nsTFixedString_CharT( char_type* data, size_type storageSize, size_type length );
+#endif

         // |operator=| does not inherit, so we must define our own
       self_type& operator=( char_type c )                                                       { Assign(c);        return *this; }
       self_type& operator=( const char_type* data )                                             { Assign(data);     return *this; }
       self_type& operator=( const substring_type& str )                                         { Assign(str);      return *this; }
       self_type& operator=( const substring_tuple_type& tuple )                                 { Assign(tuple);    return *this; }

     protected:
diff --git a/xpcom/string/public/nsTSubstring.h b/xpcom/string/public/nsTSubstring.h
--- a/xpcom/string/public/nsTSubstring.h
+++ b/xpcom/string/public/nsTSubstring.h
@@ -491,17 +491,21 @@ class nsTSubstring_CharT


     public:

         /**
          * this is public to support automatic conversion of tuple to string
          * base type, which helps avoid converting to nsTAString.
          */
+#ifdef XP_OS2 /* Workaround for GCC 3.3.x bug. */
+      nsTSubstring_CharT(const substring_tuple_type& tuple) NS_COM;
+#else
       NS_COM nsTSubstring_CharT(const substring_tuple_type& tuple);
+#endif

         /**
          * allows for direct initialization of a nsTSubstring object.
          *
          * NOTE: this constructor is declared public _only_ for convenience
          * inside the string implementation.
          */
 #ifdef XP_OS2 /* Workaround for GCC 3.3.x bug. */
@@ -517,25 +521,33 @@ class nsTSubstring_CharT
       // XXX GCC 3.4 needs this :-(
       friend class nsTPromiseFlatString_CharT;

       char_type*  mData;
       size_type   mLength;
       PRUint32    mFlags;

         // default initialization
+#ifdef XP_OS2 /* Workaround for GCC 3.3.x bug. */
+      nsTSubstring_CharT() NS_COM;
+#else
       NS_COM nsTSubstring_CharT();
+#endif

         // version of constructor that leaves mData and mLength uninitialized
       explicit
       NS_COM nsTSubstring_CharT( PRUint32 flags );

         // copy-constructor, constructs as dependent on given object
         // (NOTE: this is for internal use only)
+#ifdef XP_OS2 /* Workaround for GCC 3.3.x bug. */
+      nsTSubstring_CharT( const self_type& str ) NS_COM;
+#else
       NS_COM nsTSubstring_CharT( const self_type& str );
+#endif

         /**
          * this function releases mData and does not change the value of
          * any of its member variables.  in other words, this function acts
          * like a destructor.
          */
       void NS_FASTCALL Finalize();