Cannot read property isAttached of undefined - with firefox

[sai-tej]

Current behavior:

Cypress is not working with firefox 78.0.1

TypeError: Cannot read property 'isAttached' of undefined

Because this error occurred during a `before each` hook we are skipping the remaining tests in the current suite: `Job Failure`
      at /home/jenkins/.cache/Cypress/4.8.0/Cypress/resources/app/packages/server/lib/browsers/firefox-util.js:117:20
      at tryCatcher (/home/jenkins/.cache/Cypress/4.8.0/Cypress/resources/app/packages/server/node_modules/bluebird/js/release/util.js:16:23)
      at /home/jenkins/.cache/Cypress/4.8.0/Cypress/resources/app/packages/server/node_modules/bluebird/js/release/method.js:15:34
      at /home/jenkins/.cache/Cypress/4.8.0/Cypress/resources/app/packages/server/lib/browsers/firefox-util.js:235:40
      at tryCatcher (/home/jenkins/.cache/Cypress/4.8.0/Cypress/resources/app/packages/server/node_modules/bluebird/js/release/util.js:16:23)
      at Promise._settlePromiseFromHandler (/home/jenkins/.cache/Cypress/4.8.0/Cypress/resources/app/packages/server/node_modules/bluebird/js/release/promise.js:547:31)
      at Promise._settlePromise (/home/jenkins/.cache/Cypress/4.8.0/Cypress/resources/app/packages/server/node_modules/bluebird/js/release/promise.js:604:18)
      at Promise._settlePromise0 (/home/jenkins/.cache/Cypress/4.8.0/Cypress/resources/app/packages/server/node_modules/bluebird/js/release/promise.js:649:10)
      at Promise._settlePromises 

Desired behavior:

It should run without any errors

Test code to reproduce

Any test that runs on firefox 78.0.1 in linux fails with this error during before each.

/// <reference types="cypress" />
describe('page', () => {
  it('works', () => {
    cy.visit('https://example.cypress.io')
  })
  it('still works', () => {
    cy.visit('https://example.cypress.io')
  })
})

Versions

• Cypress 4.8.0
• Ubuntu 18.04
• Firefox 78.0.1

[sai-tej]

Work Around
The work around is to disable firefox gc interval "firefoxGcInterval": null

But now we are trusting firefox to do the right thing and not crash during the tests. This, for some reason appears to be a ticking time bomb and that concerns us. Please let me know if that's not the case.

[sai-tej]

This is same issue on ff 75

[jennifer-shehane]

Duplicate of #6813