Yes, it detects your browsers. In fact, Free Download Manager is configured to capture the downloads from your browsers with the help of an extension or through network integration. I recommend using it this way, since it's much faster to download files through the download manager instead of the built-in downloader available in the browser by default.
More information can be found on the official website: http://freedownloadmanager.org
I have used this download manager for a very long time, and it worked quite well with all the browsers I had installed on my computer.