Firefox support

[fregante]

Impossible due to w3c/webextensions#170 (comment)

I might have to do this via page on web server, but that means it won't work offline.

More ideas might come by reading w3c/webextensions#259 (comment)

Maybe executeScript + matchAboutBlank?

Maybe window.open() is fine in MV2 Firefox?

[fregante]

I might have to do this via page on web server

It's the only way that doesn't require additional files because programmatically opening data: URIs is just not allowed in Firefox: https://blog.mozilla.org/security/2017/11/27/blocking-top-level-navigations-data-urls-firefox-59/