Zoom slider (on panorama view) is not practical

On the panorama view, in the "Controls" panel, there is a slider to change the zoom level.

It is really not practical:

• with firefox, the slider is not even displayed (probably black on a black background). With chromium however, it works fine.
• even more fundamentally, a slider is not practical to use. It would be more user-friendly to have a "-" button on the left and a "+" button on the right, or something similar.