Why does she want to access my data?

Hello everyone! Today I went to FitGirl’s website with Mullvad Browser which I installed yesterday, and I instantly got this notification that she wants to access my HTML5 canvas image data. I have no idea what’s that, and I’m worried about if it’s safe to install anything from here now, also should I allow or block the request?

Hello everyone! Today I went to FitGirl’s website with Mullvad Browser which I installed yesterday, and I instantly got this notification that she wants to access my HTML5 canvas image data. I have no idea what’s that, and I’m worried about if it’s safe to install anything from here now, also should I allow or block the request?