Something that competes with electron is not electron. Non-native includes RLBox which is now going to secure Firefox according to Mozilla. Mozilla is on record regretting thunderbird's poor Integration with the Firefox stack as a trial for thunderbird devs and a tax slowing Firefox engineering.
This holding pattern has gone on and on because no one wants to establish the correct API layer to maintain as an inherent tax for Firefox engineering that enables all F/OSS to reuse the NS* stack correctly with good documentation.
In the long term this means chromium has an ecosystem and Mozilla's stable ecosystem consists of just one browser. However flawed chromium is, it has no competition for most developers and competition with WebKit for a handful.