Element is not found in Firefox even though it is definitely there #5336

I've been facing the following problem for about a week without any updates to CodeceptJS (or other dependencies) or the application code.

• test clicks on the account icon in the page header
• login form opens
• CodeceptJS should verify that a certain element exists
• it doesn't find it within 10 seconds even though it's definitely there; in open mode I can see it and inspect the DOM and it's there
• this happens 95% of time, very rarely it works
• it worked fine until about a week ago

This is the login method in the page object. The selector it doesn't find is the loginFormSelector.

    login(email, password) {
        this.openLoginForm()
        this.fillLoginForm(email, password)
    }

    openLoginForm() {
        I.waitForClickable(this.navigationLinks.responsiveLogin, 10)
        I.click(this.navigationLinks.responsiveLogin)
        I.waitForElement(this.loginFormSelector, 10) // selector is '#LoginForm'
    }

    fillLoginForm(email, password) {
        I.fillField(this.customerData.loginCustomerEmail, email)
        I.click(this.buttons.loginSubmit)
    }

The HTML looks like this:

<div id="AccountLogin">
   <section>
      <section>...</section>
      <section id="LoginForm">
         <header>...</header>
         <form>...</form>
      </section>
   </section>
</div>

What found out so far:

• no iframe
• no shadow DOM
• if I print the DOM with grabHTML in headless mode, the element is there
• if I inspect the DOM in headed mode, the element is there
• if I pause the test after it enters the login page, I can use I.seeElement in the terminal and it find the element, yet the test fails upon continuation

Does not help:

• waitForVisible instead of waitForElement
• upping the timeout to 20
• adding a hard 3 second wait
• using an older version of Firefox (I tried 145, 144 and 142)
• running it locally or in the CI pipeline does not make a difference
• using a different selector

Does help:

• going to the login page by navigating to it with I.amOnPage() instead of clicking a link to get there
• using Chrome instead of Firefox

CodeceptJS: 3.7.5
Webdriver: 9.19.2
Browser: Firefox 145 (and 144 and 142)