The latest version of Typo3 locks the frame of Quixplorer divs so you cannot resize the shape.

By editing this file:

/typo3/templates/template_page_backend.html

And adding:

###TITLE###
###META###
###CSS_INCLUDE###
###CSS_INLINE###
###JS_LIBS###
###JS_INCLUDE###
###JS_INLINE###
###HEADERDATA###
<!--###POSTJSMARKER###-->
<style type="text/css">
textarea {resize: auto;}
</style>
</head>
###BODY###
###JS_LIBS_FOOTER###
###JS_INCLUDE_FOOTER###
###JS_INLINE_FOOTER###
###FOOTERDATA###
</body>
</html>

I was able to unlock the resizing.