Mantra setting- can't upload images into slider presentations page

Please help, someone…?!?

There is a problem with uploading images to the presentations page.

I’m using the mantra 2.0.2 theme_ but I can’t upload images into slider presentations page. In the mantra settings>presentations page, I have tried (around 20 times) clicking on upload image>edit image>use this image but no file name appears in the settings form. I have ensured image size is the same as the slider dimensions and in the layout, the contents width is larger than the image size.

I’m using firefox browser