Firefox: Caret is not visible in textareas

Created by: fkling

• Sourcegraph version: Cloud
• Platform information: Firefox 100.0

Steps to reproduce:

It's actually simpler to replicate the issue in Storybook.

1. Go to https://storybook.sgdev.org/?path=/story/wildcard-textarea--text-area-examples
2. Focus a textarea (and optionally type some text)

Expected behavior:

The text carret is visible.

Actual behavior:

The caret is not visible.

https://user-images.githubusercontent.com/179026/166667061-4d215a54-ac03-4fe3-9c6a-a0e5727146ec.mp4

I already tracked down the problematic code and I'm preparing a PR.