Fix webruntime for modern Firefox versions.

[emilio]

See each individual commit for details.

FWIW, newer versions of Firefox have the site-specific browser feature, which will be a better fit and much easier to maintain for you, without having to rely on Firefox internals (this is partially Firefox's fault for not having proper embedding APIs!). But I think there's still work ongoing on that, so I haven't made use of it for now.

Instead, do a minor tweak to the existing setup that makes it work in more modern Firefox versions.

[almarklein]

Wow, thanks for this!

I should defenetely check out that new API. Thanks for the heads-up!

[thewhaleking]

This fixed my issue with Flexx. Any planned timeline on a new PyPI release containing this?

[almarklein]

I plan to do a release next week.

[almarklein]

release done today