Describe the bug
In Firefox, dragging text selections around on submission pages causes the "drop files" message to appear over the form.
Sometimes, the overlay stays there until you refresh the page (this doesn't happen consistently though)

AFAIK Chrome doesn't have this "drag text selections feature", so this bug doesn't appear.

To Reproduce
Steps to reproduce the behavior:

1. Open a new submission or edit a workspace item (e.g. https://demo7.dspace.org/workspaceitems/2376/edit) in Firefox
2. Select some text
3. Drag this selection around.
   • The "drop files" overlay appears

Expected behavior
The "drop files" should only appear when you're dragging a file.