This work is all to do with Mozilla's abilities to handle data: URLs, these are fascinating and as Mozilla has progressed it's abilities to handle progressively longer data: URLs has increased. The 5th example below wasn't possible a few iterations ago!

I wrote a little script for Boxer to convert gifs to data: URLs, it follows:

         /*********************************************
         * This  macro  will  convert  small  gifs to * 
         * BASE64 so that they might be used in  data *  
         * urls as implemented in Mozilla.            *   
         *                                            *    
         * Instructions:                              *     
         *                                            *      
         * 1.  Find  a tiny gif image and open in Hex *
         * Mode in Boxer. Save  the resulting file as *        
         * a .txt file.                               *         
         *                                            *
         * 2. Lose all the stuff that isn't Hex       *
         *                                            *          
         * 3. Run this macro.                         *
         *                                            *
         * 4.     Paste:     "data:image/gif;base64," *
         * [without  the  quotation  marks]  at   the *
         * beginning  of  the line of text you should *
         * receive.                                   *
         *                                            *
         * 5. Copy all and paste into the address bar *
         * of Mozilla.                                *
         *                                            *
         * 6. If the Image  doesn't  work it might be *
         * that the image was too  large;  tiny  gifs *
         * remember!                                  *
         *********************************************/

         macro base64(){
           int a, b, len;
           b=LineCount;
           // Move to the start of the document
           StartOfFile;
           // Lose all the white space
           ReplaceAll(" ","");
           // Move to the start of the document
           StartOfFile;
           // Make one long line of text
           for (a = 1; a < b; a++){
             EndOfLine;
             Delete;
           }
           // Replace all the Hex with Binary
           ReplaceAll("0","0000");
           ReplaceAll("1","0001");
           ReplaceAll("2","0010");
           ReplaceAll("3","0011");
           ReplaceAll("4","0100");
           ReplaceAll("5","0101");
           ReplaceAll("6","0110");
           ReplaceAll("7","0111");
           ReplaceAll("8","1000");
           ReplaceAll("9","1001");
           ReplaceAll("A","1010");
           ReplaceAll("B","1011");
           ReplaceAll("C","1100");
           ReplaceAll("D","1101");
           ReplaceAll("E","1110");
           ReplaceAll("F","1111");
           // Move to the start of the document
           StartOfFile;
           // Split the Binary into 6 byte chunks
           for (a = 1; a <= LineCount; a++){
             len = (LineLength(a)/6);
             for (b = 1; b <= len; b++){
               Right;
               Right;
               Right;
               Right;
               Right;
               Right;
               Space;
             }
           }
           // Convert the chunks into BASE64
           ReplaceAll("000000 ","A");
           ReplaceAll("000001 ","B");
           ReplaceAll("000010 ","C");
           ReplaceAll("000011 ","D");
           ReplaceAll("000100 ","E");
           ReplaceAll("000101 ","F");
           ReplaceAll("000110 ","G");
           ReplaceAll("000111 ","H");
           ReplaceAll("001000 ","I");
           ReplaceAll("001001 ","J");
           ReplaceAll("001010 ","K");
           ReplaceAll("001011 ","L");
           ReplaceAll("001100 ","M");
           ReplaceAll("001101 ","N");
           ReplaceAll("001110 ","O");
           ReplaceAll("001111 ","P");
           ReplaceAll("010000 ","Q");
           ReplaceAll("010001 ","R");
           ReplaceAll("010010 ","S");
           ReplaceAll("010011 ","T");
           ReplaceAll("010100 ","U");
           ReplaceAll("010101 ","V");
           ReplaceAll("010110 ","W");
           ReplaceAll("010111 ","X");
           ReplaceAll("011000 ","Y");
           ReplaceAll("011001 ","Z");
           ReplaceAll("011010 ","a");
           ReplaceAll("011011 ","b");
           ReplaceAll("011100 ","c");
           ReplaceAll("011101 ","d");
           ReplaceAll("011110 ","e");
           ReplaceAll("011111 ","f");
           ReplaceAll("100000 ","g");
           ReplaceAll("100001 ","h");
           ReplaceAll("100010 ","i");
           ReplaceAll("100011 ","j");
           ReplaceAll("100100 ","k");
           ReplaceAll("100101 ","l");
           ReplaceAll("100110 ","m");
           ReplaceAll("100111 ","n");
           ReplaceAll("101000 ","o");
           ReplaceAll("101001 ","p");
           ReplaceAll("101010 ","q");
           ReplaceAll("101011 ","r");
           ReplaceAll("101100 ","s");
           ReplaceAll("101101 ","t");
           ReplaceAll("101110 ","u");
           ReplaceAll("101111 ","v");
           ReplaceAll("110000 ","w");
           ReplaceAll("110001 ","x");
           ReplaceAll("110010 ","y");
           ReplaceAll("110011 ","z");
           ReplaceAll("110100 ","0");
           ReplaceAll("110101 ","1");
           ReplaceAll("110110 ","2");
           ReplaceAll("110111 ","3");
           ReplaceAll("111000 ","4");
           ReplaceAll("111001 ","5");
           ReplaceAll("111010 ","6");
           ReplaceAll("111011 ","7");
           ReplaceAll("111100 ","8");
           ReplaceAll("111101 ","9");
           ReplaceAll("111110 ","+");
           ReplaceAll("111111 ","/");
         }
    

Unfortunately data: URLs in Opera are limited to around 4100 characters so some examples won't work...

Another cool site is this one.

This isn't mine but it is excellent: This thing is great. However, I think I may have gotten a little carried away...