# Cypress v4.0.0 — Release & Upgrade Intelligence
- **Product:** Cypress (https://www.cypress.io)
- **Version:** v4.0.0
- **Released:** Feb 06, 2020
- **Impact Score:** 7/10
- **Breaking Changes:** Source flagged
- **Canonical Analysis:** https://changelogs.us/cypress/updates/v4.0.0/

## Executive Summary (TL;DR)
Cypress v4.0.0. Source highlight: Cypress 4.0.0 includes support for Mozilla Firefox browsers (beta support) and Microsoft Edge (Chromium based) browsers which is a big step forward for Cross Browser Testing in Cypress. We've also updated many of the underlying tools behind Cypress that bring new powerful features.

## Breaking Changes & Deprecations
- Breaking Changes:** **:warning: Please read our [Migration Guide](https://on.cypress.io/migration-guide) which explains the changes in more detail and how to change your code to migrate to Cypress 4.0.**
- - Mocha, Chai, and Sinon.JS has been upgraded which includes a number of breaking changes and new features. Addresses [#2528](https://github.com/cypress-io/cypress/issues/2528), [#2529](https://github.com/cypress-io/cypress/issues/2529), [#2866](https://github.com/cypress-io/cypress/issues/2866).

## New Features
- Mocha, Chai, and Sinon.JS has been upgraded which includes a number of breaking changes and new features. Addresses #2528, #2529, #2866.
- Added Cross Browser Testing Guide with helpful CI strategies to consider when running tests across multiple browsers.
- Added `Cypress.isBrowser()` doc.
- We added types for plugin events. Addresses #6322.
- Added `@benmalka/foxdriver`. Addressed in #1359.
- Added `firefox-profiler`. Addressed in #1359.

## Bug Fixes
- A test or suite appended with an `.only` when multiple tests or suites contained the same title now run correctly. Fixes #5345.
- The `.its()` command now properly supports 0 as a value for indexes or object keys. Fixes #6216.
- We fixed a broken 'Learn more' link within the Node.js Version panel of the Test Runner Settings. Addresses #6237.
- You can print debug information about the memory & CPU usage of Cypress, which can be accessed by enabling the `cypress:server:util:process_profiler` debug stream. Addresses #6169.
- Upgraded `debug` from `2.15.1` to `4.0.1`. Addressed in #4226.