When I drag a file onto SOM to upload, the file opens in the browser instead. Why???

We've run into this several times, and while it doesn't make much sense, it has to do with the Zoom level in the Chrome Browser. 

Any time you see this, just go into your Chrome settings - click this button in the upper right:

Then on the Settings pane that opens, locate the Zoom section and restore it to 100%

Then you can drop files again!