Applet tile engine - Java-Gaming.org

I am not trying to make a game with an applet, just do some simple tile rendering things. I have come up with a nice effect, animated tiles too. The only problem is sometimes it loads in my browser and sometimes it does not. I am currenly using firefox, if I open the applet with ie it loads more often but still not all the time. I posted my full source and was wondering if someone can tell me why this is happening. Thanks.

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import java.applet.*;
import java.awt.*;
import java.awt.event.*;

public class Tile_engine extends Applet implements KeyListener, Runnable {

  private int keyPressed = -1;
  private int screenX = 0;
  private int screenY = 0; 
  private final int TILE_MAX = 11;
  private final int TILE_SIZE = 32;
  private final int APPLET_WIDTH = 640;
  private final int APPLET_HEIGHT = 480; 
  private final int SKY = 0;
  private final int CLOUD_1 = 1;
  private final int CLOUD_2 = 2;
  private final int RED_BRICKS = 3;
  private final int GRASS = 4;
  private final int DIRT = 5;
  private final int STONE = 6;
  private final int QBOX1 = 7;
  private final int QBOX2 = 8;
  private final int QBOX3 = 9;
  private final int QBOX4 = 10;
  private final int MAP_ROWS = 15;
  private final int MAP_COLS = 65;
  private Image background = null;
  private Image buffer = null;
  private Graphics bgBuff;
  private Graphics bufferg;
  private Image[] tile = new Image[TILE_MAX];

  private final int map[][] = 
    {{0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,6,6,6,6,6,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0},
     {0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,7,7,7,7,0,0,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,6,0,0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,1,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,7,0,0,0,0,0,0,0,0,0,0,0,0,6,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,3,3,3,3,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,3,3,3,3,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,3,3,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,3,3,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,6,6,6,6,6,0,0,0,0,0,0,0,0,0,0,0,0,0,0,3,3,0,0,0,0,0,0,0},
     {0,0,7,7,7,0,0,0,0,0,0,0,3,3,3,3,0,0,0,0,0,0,0,0,0,0,4,0,0,0,0,0,0,0,0,0,0,6,6,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,0,3,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,5,0,0,0,0,0,0,0,0,0,3,6,6,0,0,0,0,4,4,4,4,4,4,4,4,4,4,4,0,0,0,0,0,0,0,0,0,0,0},
     {0,0,0,0,0,0,3,3,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,4,0,5,0,0,0,0,0,0,0,0,0,3,6,6,0,0,0,0,5,5,5,5,5,5,5,5,5,5,5,0,0,0,0,0,0,0,0,0,0,0},
     {4,4,4,4,4,4,4,4,0,0,4,4,4,4,4,4,4,4,4,4,4,4,0,0,5,0,5,0,0,4,4,4,0,0,0,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,4,4,4,4,6,6,6,4,4,4,4},
     {5,5,5,5,5,5,5,5,0,0,5,5,5,5,5,5,5,5,5,5,5,5,0,0,5,0,5,0,0,5,5,5,0,0,0,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,0,0,0,5,5,5,5}};
   
  
  public void init( ) {
    tile[SKY] = getImage(getDocumentBase(), "sky.png");
    tile[CLOUD_1] = getImage(getDocumentBase(), "cloud1.png");
    tile[CLOUD_2] = getImage(getDocumentBase(), "cloud2.png");
    tile[RED_BRICKS] = getImage(getDocumentBase(), "redBricks.png");
    tile[GRASS] = getImage(getDocumentBase(), "grass.png");
    tile[DIRT] = getImage(getDocumentBase(), "dirt.png");
    tile[STONE] = getImage(getDocumentBase(), "stone.png");
    tile[QBOX1] = getImage(getDocumentBase(), "qbox1.png");
    tile[QBOX2] = getImage(getDocumentBase(), "qbox2.png");
    tile[QBOX3] = getImage(getDocumentBase(), "qbox3.png");
    tile[QBOX4] = getImage(getDocumentBase(), "qbox4.png");

    buffer = createImage(TILE_SIZE * MAP_COLS, TILE_SIZE * MAP_ROWS);
    bufferg = buffer.getGraphics();

    addKeyListener(this); 

    if(buffer != null) {
      int tile_id;
      for(int y=0;y<MAP_ROWS;y++) {
        for(int x=0;x<MAP_COLS;x++) {
          tile_id = map[y][x]; 
          bufferg.drawImage(tile[tile_id], x * TILE_SIZE, y * TILE_SIZE, this);
        }
      }
    } 

  }

  public void start( ) {
    Thread th = new Thread(this);
    // start this thread
    th.start(); 
  }

  public void run( ) {
    Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
    while(true) {
      animate_tiles();
    
      try {
   Thread.sleep(200);
      } catch(InterruptedException ex) {
      }
      Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
    } 
  }
  
  public void animate_tiles( ) {
    int tile_id;
    
    for(int y=0;y<MAP_ROWS;y++) {
      for(int x=0;x<MAP_COLS;x++) {
        tile_id = map[y][x]; 
      
        switch(tile_id) {
          case QBOX1: map[y][x] = QBOX2; break;
          case QBOX2: map[y][x] = QBOX3; break;
          case QBOX3: map[y][x] = QBOX4; break;
          case QBOX4: map[y][x] = QBOX1; break;
          default: break; //not needed  
        }
      }
    }
  }

  public void paint(Graphics g) {}

  public void update(Graphics g) {
    //animate_tiles();

    if(buffer != null) {
      int tile_id;
      for(int y=0;y<MAP_ROWS;y++) {
        for(int x=0;x<MAP_COLS;x++) {
          tile_id = map[y][x]; 
          bufferg.drawImage(tile[tile_id], x * TILE_SIZE, y * TILE_SIZE, this);
        }
      }
    } 

    paint(bufferg);
    g.drawImage(buffer, screenX, screenY, this); 
    repaint(); 
  }

  public void keyReleased( KeyEvent e ) { }
  public void keyPressed( KeyEvent e ) { }
  public void keyTyped( KeyEvent e ) {  
    char c = e.getKeyChar();
    if(c == 'z') { screenX+=5; }
    else if(c == 'c') { screenX-=5; }
  }  
}