Let me first thank you for this plugin it has saved me many hours. Its ease of configuration is a joy.
I would like to do my bit to improve this plugin so I thought I ma just record my findings.
If the following attributes scolling="no", frameborder="no" and allowTransparency="true" are removed from line 103 the HTML validates as HTML5. It seems to look fine for IE7 onwards and the recent version of other browsers like Firefox and Google Chrome.
I am not sure how easy this is but it it possible to make the font-size for the FB messages configurable?
Thank you once again for your plugin and if there are no problems with the changes I have suggested perhaps the next release could incorporate this.