Firefox 78 for developers

This article provides information about the changes in Firefox 78 that will affect developers. Firefox 78 was released on June 30, 2020.

See also New in Firefox 78: DevTools improvements, new regex engine, and abundant web platform updates on Mozilla hacks.

Changes for web developers

Developer Tools


Network Monitor

Other tools

  • The Accessibility inspector is out of beta. You can use it to check for various accessibility issues on your site. (bug 1602075)
  • Uncaught promise errors now provide all details in the Console, including their name and stack. (bug 1636590)





Service workers


  • Wasm Multi-value is now supported, meaning that WebAssembly functions can now return multiple values, and instruction sequences can consume and produce multiple stack values (bug 1628321).
  • WebAssembly now supports import and export of 64-bit integer function parameters (i64) using BigInt from JavaScript (bug 1608770).

TLS 1.0 and 1.1 removal

Changes for add-on developers

  • browsingData.removeCache and browsingData.removePluginData now support deleting by hostname. (bug 1636784).
  • When using proxy.onRequest, a filter that limits based on tab id or window id is now correctly applied. This could be useful for add-ons that want to provide proxy functionality just in just one window.
  • Clicking within the context menu from the "all tabs" dropdown now passed the appropriate tab object. In the past, the active tab was erroneously passed.
  • When using with the saveAs option, the recently used directory is now remembered. While this information is not available to developers, it is very convenient to users.

Older versions