[PWA-513] Fix Dropdown arrows in Firefox

[davemacaulay]

Description

Ensure dropdown arrows are always displayed in Firefox when auto complete is used

Related Issue

https://jira.corp.magento.com/browse/PWA-513

Acceptance

Verification Stakeholders

@jimbo
@dhaecker

Specification

Verification Steps

Pre-condition - Test in Firefox browser
Steps -

1. Add a producto cart and go to /checkout page
2. Select a saved US address to fill shipping info.

Screenshots / Screen Captures (if appropriate)

Checklist

• I have added tests to cover my changes, if necessary.
• I have updated the documentation accordingly, if necessary.

[PWAStudioBot]

	Messages
📖	Access a deployed version of this PR here. Make sure to wait for the "pwa-pull-request-deploy" job to complete.
📖	DangerCI Failures related to missing labels/description/linked issues/etc will persist until the next push or next nightly build run (assuming they are fixed).
📖	Associated JIRA tickets: PWA-513.

Generated by 🚫 dangerJS against dcb90ac

[devops-pwa-codebuild]

Performance Test Results

The following fails have been reported by WebpageTest. These numbers indicates a possible performance issue with the PR which requires further manual testing to validate.

https://pr-2455.pwa-venia.com : LH Performance Expected 0.85 Actual 0.57, LH Best Practices Expected 1 Actual 0.92
https://pr-2455.pwa-venia.com/venia-tops.html : LH Performance Expected 0.75 Actual 0.36, LH Best Practices Expected 1 Actual 0.92
https://pr-2455.pwa-venia.com/valeria-two-layer-tank.html : LH Performance Expected 0.8 Actual 0.47, LH Accessibility Expected 0.9 Actual 0.89, LH Best Practices Expected 1 Actual 0.92

[jimbo]

Copying my comment from the other PR:

Makes sense. DOM order should normally be enough, but I can see how one browser or another could have trouble with ordering when one of the siblings is a replaced element.

[dhaecker]

QA approved