HTML5 canvas access exception UI inaccessible on some sites

The UI element in the URL bar for enabling HTML5 canvas access is only shown when LW determines that the current page is trying to access the canvas. There is no other readily accessible UI to allow canvas access for a specific page/domain/... that I could find.

Regardless of the "Silently block canvas access requests" and related settings, there are situations that make it impossible to enable such an exception.

Today, I found a readily available test case: https://gravatar.com/

After uploading an image, one is asked to crop it using an interactive UI that works well and does not show any canvas access warnings. When clicking "Crop Image" to confirm the chosen image clipping, only then will the page / some script / ... try to access the canvas to read the selected image data (or uses the canvas to process the image in some way behind the scenes). This causes the URL bar canvas exception element to pop up, however the logic on gravatar.com immediately navigates away from the current page, which in turn causes the canvas access exception UI to immediately disappear again. The result is that the chosen image is committed as the usual vertically striped "access denied" image instead.

I would suggest a more accessible UI to configure (and remove) canvas exceptions for specific domains; and/or - in the "do not silently block" mode - making the canvas access request modal, so any scripts on the page can only continue after the user has made a definite choice.

Showing the canvas access exception UI "after it's too late" and not even keeping it on screen to try again leads to situations that are impossible to solve from the user's perspective.