Isn't working in Firefox

I just found your solution and tested it in Chromium and Firefox (v 54.0.1). The latter isn't working properly: after pressing OK in the selection dialog the whole page becomes white and stays white. Resetting to 0 (off) let the original site reappear. May looks like some issue with the filtering!?
 
By the way: Thanks for providing your solution! *thumbsup*