Free Download Manager works with most major web browsers, including Opera 12 and earlier. However, Opera 15 has come out, based on the same Chromium code as Google Chrome. It has a different Add-On/extension API than earlier versions of Opera. Earlier versions of Opera and Opera 15 can coexist on the same computer. In fact if you install Opera 15 on a computer that has Opera 12, it will import some settings from the Opera 12 installation, but you will end up with 2 separate versions of Opera both installed on your computer. Many Opera users are not fans of the new Opera 15 and are sticking with Opera 12 but others are getting the new version.

So as far as Free Download Manager is concerned, Free Download Manager needs to develop a browser add-on to integrate with Opera 15 and future versions of Opera, but it should also KEEP the existing browser add-on for Opera 12 and earlier, since it seems many Opera users are sticking with Opera 12 and earlier, and there is no reason to remove support for something if it works fine. So the support for Opera 12 and earlier, which works fine, should stay the way it is, and my feature request is to add support to integrate Free Download Manager with Opera 15 and later.

Anyway this should be easy to implement because Opera 15 and later has an extension format that is virtually identical to Google Chrome. So the existing Free Download Manager extension for Google Chrome just needs to be slightly repackaged and then installed with Opera 15 and later and it should be good to go, but this will require the Free Download Manager installer and program being able to detect installations for Opera 15 and later and know the proper location to install the extension. But that shouldn't be too different from detecting installations of other browsers.

But yeah, Opera 15 is basically just a rebranded version of Google Chrome at this point and pretty much everything works the same (it doesn't just share the same Blink rendering engine that was forked from WebKit, it shares pretty much everything from the Chromium project), so integrating Free Download Manager into it should work exactly the same as with Google Chrome and you can probably use the existing code for integrating with Google Chrome, with very few modifications.

EDIT: Apparently Free Download Manager only works with Opera versions 6.x - 10.x, I was mistaken about it supporting Opera 11.x - 12.x. However, the 15.x and higher extension interface is virtually identical to Google Chrome's extension interface so my feature request for Opera 15.x and higher support still stands (probably all that is needed is to install the existing Google Chrome extension into the Opera 15.x extensions directory).

You weren't mistaken - although is stated that it officially supported Opera 6 - 10, I had it working with no intervention on Opera 12 as well. And until I read your post I had no idea it was not working on 15 - so I naturally had to test, and sure enough, no go.

Since you say it is based on Chrome's webkit I'm gonna try forcing it to recognize the Chrome plugin and see if it works....