I tried to contribute via PayPal to Multifox from the Mozilla Add-on
page (https://addons.mozilla.org/en-US/firefox/addon/multifox/), but
was unable to do so (because I had 3rd party cookies disabled). OK,
that's one problem.
But the Multifox page issue is that I got just a blank screen overlay
because of PayPal X-Frame-Options on the response from PayPal --
basically, it looks like the PayPal complaint page is being loading
into some non-PayPal frame, which PayPal's X-Frame-Option forbids.
The complaint in the web console is
Load denied by X-Frame-Options:
not permit cross-origin framing.
The Response Headers
Please consider fixing this, so that others are not presented with a
silent grey overlay if there is a problem trying to donate via PayPal.
Thanks for a great! add-on. /Jskud
It seems to be Mozilla bugs. See:
Closing as it is not specific to Multifox.