Opera Send Link By Mail Bookmarklet:

Function: Creates and opens a mailto URI containing the document's title 
(for the subject) and the document's location (for the body). 

Modes: At the end of the javascript URI below, you can set the mode. The default is 
"normal".

normal: Document's location comes out as <http://example.com/> in the body 
field.

Modes specific to Thunderbird when you have HTML composition on in 
Thunderbird and use Thunderbird 2.x, or use Thunderbird 3.x with the 
thunderbird.exe -compose "body=value,subject=value" command syntax to pass 
a mailto URI to Thunderbird 3.x:

tbird1: Document's location comes out as an HTML link encased in brackets 
whose HTML source would be 
&lt;<a href="http://example.com/">http://example.com/</a>&gt;

tbird2: Document's location comes out as <http://example.com/> whose HTML 
source would be &lt;http://example.com/&gt;

Here's the javascript URI:

javascript:(function(mode)%7Bfunction%20enc(s)%7Btry%7Breturn%20encodeURIComponent(s)%7Dcatch(e)%7Breturn%20%22Opera%2520received%2520an%2520error%2520while%2520percent-encoding%2520the%2520data%22%3B%7D%7Dvar%20sub%3Denc(document.title)%3Bvar%20loc%3Ddocument.location%3Bvar%20body%3Denc(%22%3C%22%2Bloc%2B%22%3E%22)%3Bif(mode%3D%3D%22tbird1%22)%7Bbody%3Denc('%26lt%3B%3Ca%20href%3D%22'%2Bloc%2B'%22%3E'%2Bloc%2B'%3C%2Fa%3E%26gt%3B')%3B%7Delse%20if(mode%3D%3D%22tbird2%22)%7Bbody%3Denc(%22%26lt%3B%22%2Bloc%2B%22%26gt%3B%22)%3B%7Dvar%20uri%3D%22mailto%3A%3Fsubject%3D%22%2Bsub%2B%22%26body%3D%22%2Bbody%3Bwindow.open(uri)%3B%7D)(%22normal%22)%3B

Here's the compressed source:

(function(mode){function enc(s){try{return encodeURIComponent(s)}catch(e){return "Opera%20received%20an%20error%20while%20percent-encoding%20the%20data";}}var sub=enc(document.title);var loc=document.location;var body=enc("<"+loc+">");if(mode=="tbird1"){body=enc('&lt;<a href="'+loc+'">'+loc+'</a>&gt;');}else if(mode=="tbird2"){body=enc("&lt;"+loc+"&gt;");}var uri="mailto:?subject="+sub+"&body="+body;window.open(uri);})("normal");

Here's the source of the javascript URI:

(function(mode) {
    function enc(s) {
        try {
            return encodeURIComponent(s)
        } catch (e) {
            return "Opera%20received%20an%20error%20while%20percent-encoding%20the%20data";
        }
    }
    var sub = enc(document.title);
    var loc = document.location;
    var body = enc("<" + loc + ">");
    if (mode == "tbird1") {
        body = enc('&lt;<a href="' + loc + '">' + loc + '</a>&gt;');
    } else if (mode == "tbird2") {
        body = enc("&lt;" + loc + "&gt;");
    }
    var uri = "mailto:?subject=" + sub + "&body=" + body;
    window.open(uri);
})("normal");

Note: When using window.open to open the mailto URI, Opera will undo some of
the percent-encoding done by encodeURIComponent above. Opera will take %3A and 
%2F and decode them to :/ on you. This means Opera will pass:

mailto:?body=%3Chttp://www.opera.com/%3E

instead of the expected:

mailto:?body=%3Chttp%3A%%2F%2Fwww.opera.com%2F%3E

to the mail client.