What is the problem?
I use Firefox as browser. During file uploading with drag and drop, the drop targets dissappear imediately. They reappear when moving the cursor and are active as dropping while moving works often.
What did you already try to solve it?
Chrome and Chromium work fine.
Same version FF works fine on MacOS
Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware,
serial.log or output on terminal tab, ...'
The snappy web interface for your 3D printer
The ready-to-go Raspberry Pi image with OctoPrint
Version 0.15.1, running on Raspberry Pi 3 Model B Plus Rev 1.3/