uses ddeman;
     
function GetURL(Browser: string): string;
var
   Client_DDE: TDDEClientConv;
   temp: PChar;
begin
   Result := '';
   Client_DDE:= TDDEClientConv.Create( nil );
   with Client_DDE do
    begin
     SetLink(Browser, 'WWW_GetWindowInfo');
     temp := RequestData('0xFFFFFFFF');
     Result := StrPas(temp);
    // Return only the URL part
     Delete(Result, Pos(',', Result), Length(Result)-Pos(',', Result)+1);
     // Remove quotes
     Delete(Result, 1, 1);
     Delete(Result, Length(Result), 1);
     // ************
     StrDispose(temp);
     CloseLink;
    end;
   Client_DDE.Free;
end;
     
procedure SetURL(URL, Browser: String);
var
    Client_DDE: TDDEClientConv;
begin
    Client_DDE := TDdeClientConv.Create(nil);
    with Client_DDE do
    begin
      SetLink( Browser, 'WWW_Activate' );
      RequestData('0xFFFFFFFF');
      SetLink( Browser, 'WWW_OpenURL' );
      RequestData(URL  + ',,0xFFFFFFFF,0x3,,,');
      CloseLink;
    end;
    Client_DDE.Free;
end;

...

SetURL('http://forum.sources.ru/','FireFox');