The example test case is on your homepage: http://piro.sakura.ne.jp/xul/textlink/index.html.en#testcases
There is a nice feature that lets users not to aim at exactly the beginning of a word if they select some word/text - you can double click the word to select it, or you can double click that word and without releasing the 2nd click move the cursor to select more then one word.
Now try to use it on the test case: as a result, when you release the 2nd click, after selecting the whole paragraph "Test cases" - Text Link will work out and it will recognize that the selected text contains some links and it will open the first of them.
The expected behavior is that TextLink shouldn't work out in this case, as it is obvious that I'm not selecting a link, I'm selecting just some text.
Forbid "dblclick" handling, if mouse was moved
Should fix #11
Main idea: remember "double mousedown" position and compare it with "double mouseup" position.