I've been trying dock my palette window for a bit, and have been unable to do so. I've looked around and found some other questions about this topic, but none of the solutions work for me. One of the ways people have said works to dock the window is to double click the top of the floating window. All this does for me is make that window full screen. The other solution is that I need to drag the window off of musescore, and then slowly drag is back on until the area gets highlighted in blue, but I've been trying that for a good 20 minutes with no results. I'm using the most current update of musescore (as of March 10th), and am on MacOS 10.12.6. Thanks and have a nice day!
Edit: Okay, so I've been able to dock the window by reverting Musescore to factory settings, but that resets a lot of things that people like to customize (e.g., custom palettes). This is a working solution, though not very elegant.