I have FDM 1.45 and my browser is Opera 7.54.
Some of the download links on Download.com will start up automatically, but some won't.
For instance, clicking "Download Now" for Twister 2.6.5, which is the following link,

javascript:downloadNow('http://www.twistermp3.com/download/twisterfree.exe','http://dw.com.com/redir?pid=10338438&merid=111180&mfgid=111180&ltype=dl_dlnow&lop=link&edId=3&siteId=4&oId=3140-2166_4-10338438&ontId=2166_4&destUrl=http://www.download.com%2F3001-2166_4-10338438.html','0');

FDM starts the download automatically as it should.
But, if I click "Download Now" for Copernic Desktop Search 1.1, which is this link,

javascript:downloadNow('http://software-files.download.com/software/10329016/10314159/3/copernicdesktopsearch.exe?lop=link&ptype=3120&ontid=2001&siteId=4','http://dw.com.com/redir?pid=10329016&merid=52087&mfgid=52087&ltype=dl_dlnow&lop=link&edId=3&siteId=4&oId=3120-2379_4-10329016&ontId=2379_4&destUrl=http://www.download.com%2F3001-2379_4-10329016.html','0');

Opera displays the download dialog box telling me that this file is MIME Type "application/x-msdownload" and File extension "exe" and I can select either Open, Save, etc.
For this MIME Type/File extension, Opera is supposed to use the FDM plugin, not "Show download dialog".
Anyway, if I click "Open" to open with FDM, the word "Click" is displayed.
Clicking on that, a "Plugin required" dialog box is displayed. It tells me that the File is "3001-2379_4-10329016.html"
Why does Opera not use the FDM plugin as it should and why is the correct file name not being recognized?
Does something need to be in the "Referrer" box under Default download settings\Protocol?

Please ask your question in the Opera's support forum.

Thanks for your advice, Alex
I was told to report this as an Opera bug, which I did.
Hopefully, the Opera developers will take care of it.