Firefox 46 have a wrong behavior on my Linux Mint 17. In the upload windows the mouse keeps the focus on the first selected file and it selects all the files it pass over. It is the behavior you expect to have when you select multiple file keeping the mouse left button pressed. Moreover, if I select a directory in the directory panel of the upload window, I cannot move the focus on the file panel. The only way I can do it is using the tab button on keyboard. I didn't have this problem with the previous Firefox versions.