We’re in the process of updating the documentation for Zotero 5.0. Some documentation may be outdated in the meantime. Thanks for your understanding.
Zotero's support for running translators outside of Firefox (Gecko) is provided by browser plugins that implement all or part of the translator infrastructure in another browser environment. There are currently such connectors for Apple's Safari and Google's Chrome browsers, and there are plans to create one for some versions of Microsoft's Internet Explorer at a later date.
See also: Connector changelog
This page is woefully incomplete, and should be expanded with a better description, by the time the next stage of Zotero Everywhere is widely released. We should have details on what makes a translator connector-agnostic, on testing connectors, and perhaps a brief overview of what it would take to make a new connector.