the hashes are different to the hashes when CanvasBlocker is disabled
the number of differences stays the same when CanvasBlocker is disabled
if "refresh" is clicked nothing must change
upon page reload the hashes change (depending on CanvasBlocker settings - e.g. not in the stealth preset)
Firefox 68 does only offer integer precision in TextMetrics and therefore less fingerprinting potential. CanvasBlocker only changes values if they are no integer and therefore point 1 and 4 are not true in Firefox 68.