The downloader component was removed due to recent Adobe Flash updates causing the functionality to become increasingly less reliable. You can download the previous version of Adapter for Mac from the link below, if you'd prefer. However, the downloader may or may not work for some Flash videos. It seems to work on HD vids but not on the lower resolution ones such as 240p and 320p. You can sometimes force a download by clicking on the gear icon to change the video quality to one that suits your needs.
Adapter v.1.4.2 for Mac
Just be sure to not update the software in order to keep the downloader feature. You can choose Skip this Version in any software update windows, and Adapter preferences even has a checkbox to disable auto-check for updates.
We plan to make the older version of Adapter for Windows available for direct download soon too for any one needing the web downloader