test with FF Fission (iframe isolation)

[balmas]

See https://blog.mozilla.org/addons/2020/07/24/extensions-in-firefox-79/?utm_source=newsletter&utm_medium=email&utm_campaign=about-addons-jul-2020#Fission

"The Firefox platform team has been working on a new security architecture that isolates sites from each other, down to separating cross-origin iframes from the tab’s process. This new model, nicknamed Fission, is currently available for opt-in testing in Nightly. The platform team is planning to begin roll-out to Nightly and Beta users later this year."

I think we should be fine because all iFrame communication is either via links or postMessage but we should test to be sure.

@kirlat I'm giving you this one to work on as you have time.