Hello, (sorry for my bad English, I speak French) I use Free Download Manager for so long that I don't even remember the first version I used and when it was. ^^
But now, I have decided now to help you by suggesting some features.

First, I am a big Firefox user, but I also use sometime others browsers and it appear to me that you don't support Opera 11 and Chromium, I didn't look but I guess you working on a feature for Opera 11 already but I was surprised that FDM works on Chrome but not on Chromium, they are so much like, he must not be hard to make it works.

I also download a lot on filesharing website and some of them are not compatible with Firefox/FDM, Firefox can downloading the files fine alone but FDM can't I got just a webpage to the end of the downloading process. I can't make a precise list of witch website doesn't work, but I can give you some that may not work :
hotfile.com
(www.)filesonic.com
ul.to
(www.)fileserve.com
file4sharing.com
(www.)filejungle.com
fp.io
filepost.com
(www.)wupload.com
(www.)uploadstation.com

This is it, I think I don't have anything to ad, hope that my suggestion can help you for the next FDM's version. And I wish you guys can keep FDM like he was always for me : the best Download Manager.
Keep the good work guys !!! ^^