Regex Not work

This regex not work, when I put this code:
(?<=<div class=”fb”>)(.*\n?)(?=</div>)

into “Search pattern” Field, it is change the code to something messy. it makes the regex not work. can you fix this?

Coz this plugin is great if only the regex is work well.

http://wordpress.org/extend/plugins/html-regex-replace/