'Cypress runner gives me a 404 when using Firefox browser

This issue seems somewhat related to Cypress.io: Server Error | 404 - File or director not found but the solution provided did not work for me.

I can run my tests in Cypress runner fine with Chrome, Electron and Edge but when I attempt to run a test in Firefox I'm getting a 404. I'm using FF 86

I enabled experimentalSourceRewriting in my cypress.json file but it's still failing.

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Solution 1:[1]

The issue was with Zscaler and some scripts that were changing the Firefox proxy.

Sources

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Source: Stack Overflow

Solution Source
Solution 1 onimougwo