Forum rules
Please always mention the name/domain of the website in question in your topic title.
Please one website per topic thread (to help keep things organized). While behavior on different sites might at first glance seem similar, they are not necessarily caused by the same.
Please try to include any relevant output from the Toolkit Error Console or the Developer Tools Web Console using the following procedure:
Clear any current output
Navigate or refresh the page in question
Copy and paste Errors or seemingly relevant Warnings into a single [ code ] block.
This is a known issue: UXP #1691
It's been covered a million times. For now, implore the web site developer(s) to target standards-compliant browsers, not experimental ones.