12224 ui test about firefox preview

[isabelrios]

PR for #12224 Trying to fix the test, if not it will be disabled so that it does not interfere with dev process

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

After merge

• Milestone: Make sure issues finished by this pull request are added to the milestone of the version currently in development.

To download an APK when reviewing a PR:

1. click on Show All Checks,
2. click Details next to "Taskcluster (pull_request)" after it appears and then finishes with a green checkmark,
3. click on the "Fenix - assemble" task, then click "Run Artifacts".
4. the APK links should be on the left side of the screen, named for each CPU architecture

[isabelrios]

@AaronMT not sure if there is a better way than disabling the check in the support website text, since that is going to change according to the Android version. Now it shows What's new in Firefox for Android 79 but if we check that text we would need to update the test each time a new version is released...
I have run the test this way 50 times and no failures..
The PR still contain the flank changes in case I have to run changes more times, but I will remove that part before merging...

[AaronMT]

Looks fine to me (cc @sv-ohorvath might have an idea on other text to check here?). Remember to not merge the flank yml change.