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merged 1 commit into from
Aug 5, 2025

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MikeMcC399
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Situation

Firefox 141.0 and above is not compatible with versions of Cypress below 14.1.0 and this is not specifically mentioned on https://docs.cypress.io/ (see cypress-io/cypress#32148).

The Get Started > Install Cypress > System requirements section lists only base system requirements without mentioning browsers. For browser information, readers have to find and consult with the page References > Launching Browsers where the Firefox version restriction is however not mentioned.

The related section References > Launching Browsers > Browsers > Firefox Browsers > Webdriver BiDi and CDP Deprecation is planned for removal in Cypress 15.

Change

Add a "Browsers" section to the page Get Started > Install Cypress > System requirements section.

Suggestion

Review the plans to remove the section References > Launching Browsers > Browsers > Firefox Browsers > Webdriver BiDi and CDP Deprecation in Cypress 15 and consider reworking it based on the current situation. Perhaps retitle to "Webdriver CDP to BiDi Migration" given that CDP is no longer just deprecated, but removed entirely?

Reference

Source Date
Bugzilla 1882096 - Remove CDP support from Remote Agent Feb 26, 2024
Cypress 14.1.0 - changelog Feb 25, 2025
WebDriver BiDi Becomes the Default for Cypress with Firefox Feb 26, 2025
CDP Retirement in Firefox Jun 2, 2025
Firefox 141 for developers - release notes Jul 22, 2025

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@MikeMcC399 MikeMcC399 marked this pull request as ready for review August 4, 2025 09:45
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@jennifer-shehane jennifer-shehane left a comment

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Feels a bit odd to add to the install. As the install is not where this requirement is needed. It's at the launching browsers step that it would fail.

I would say this section certainly needs updating to include the Firefox 141 CDP no longer working. I don't think that env var would work anymore. https://docs.cypress.io/app/references/launching-browsers#Webdriver-BiDi-and-CDP-Deprecation

It's always hard to figure out where to put 'We don't support this anymore' info because you want to stay current. 🤔

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MikeMcC399 commented Aug 4, 2025

@jennifer-shehane

Feels a bit odd to add to the install. As the install is not where this requirement is needed. It's at the launching browsers step that it would fail.

It felt right to add it to this page, because there are two major sections to Get Started > Install Cypress

  • Install
  • System requirements

and the browser information belongs to "System requirements". Similar to the section Linux Prerequisites, you can install Cypress without the Linux prerequisites (I tested this): you just can't run Cypress without them installed. So, if you don't have the right browsers installed, you won't be able to run against them.

Merging this PR would mean that compatibility information is all on one page, for easier reference.

I would say this section certainly needs updating to include the Firefox 141 CDP no longer working. I don't think that env var would work anymore. https://docs.cypress.io/app/references/launching-browsers#Webdriver-BiDi-and-CDP-Deprecation

It's always hard to figure out where to put 'We don't support this anymore' info because you want to stay current. 🤔

Yes, this is difficult, because the Cypress documentation is only supposed to cover the latest version, apart from the Changelog and Migration Guide and the history tables at the bottom of some pages.

Perhaps just defer trying to address this point until after Cypress 15 is released? Firefox <=134, which would need the environment variable, no longer falls into the category of 3 latest versions supported. A short note would still be helpful to confirm the need to update / upgrade though.

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@jennifer-shehane

The Cypress 15 beta docs should probably be discussed elsewhere, even though I brought up the topic here. This PR is for Cypress 14 as the current latest version.

But just to round off the discussion:

  • Firefox releases 134 and below, which were released before BiDi support was added to Firefox, are no longer supported by Cypress according to the "the latest 3 major versions" rule (currently allows for Firefox 141, 140 & 139).
  • Attempting to test against Firefox 134 with Cypress 15 beta results in the error message:

    Cypress does not support running Firefox version 134 due to lack of WebDriver BiDi support. To use Firefox with Cypress, install version 135 or newer.

  • Setting FORCE_FIREFOX_CDP has no effect in Cypress 15 beta. CDP for Firefox has been removed.

@jennifer-shehane jennifer-shehane merged commit 8628816 into cypress-io:main Aug 5, 2025
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@MikeMcC399 MikeMcC399 deleted the browser-support branch August 6, 2025 05:15
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Firefox failing to start with Firefox 141 and pre-Cypress 14
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