A bookmarklet , also called a favelet, is a small piece of javascript  in a bookmark that you click to do something useful. The following examples work in Firefox. They may also work in other browsers. 
Hootlet for Hootsuite.com 
More Bookmarklets 
	Creating a Bookmarklet 
You can create a bookmarklet  like any other bookmark. Here is the method to create one in the Firefox "Personal Toolbar".  
Highlight the bookmarklet code (Select All), then type CTRL+C  (hold the CTRL key while typing C) to copy it to the Clipboard.
 Create a New Bookmark (open All Bookmarks for editing).
 Beside Name in the Properties box, type a short name for the function.
 Beside Location, type CTRL+V  to paste the text you just copied.
  
	
Instantly shrinks a page to fit your screen width.
	
The tool prompts you for an equation and displays the result.
(CTRL+C to copy) 
javascript:expr=prompt('Formula... eg:  2*3 + 1/2 ','');if(expr){with(Math){evl=parseFloat(eval(expr))};if(isNaN(evl)){alert('Not a number!')}else{void(prompt('Result:',evl))}}else{void(null)}
 
 
	
U.S. dollars you enter is converted to Canadian dollars at
OANDA.COM .
(CTRL+C to copy) 
javascript:q=document.getSelection();for(i=0;i/textarea>
  
 
	
Displays a web page of coloured boxes using 216 standard web colours.
(CTRL+C to copy) 
javascript:t='';c=new Array('00','33','66','99','CC','FF');for(i=0;i<6;i++){t+='';for(j=0;j<6;j++){t+='';for(k=0;k<6;k++){L=c[i]+c[j]+c[k];t+=''+L}t+='  '}t+='
'};with(document){write(t);void(close())}
 
 
Hootlet for Hootsuite.com 
More Bookmarklets