docs(style-focus): button focus macos firefox

[ApplY3D]

Changes proposed in this pull request:

• updated info about button focus in Firefox on macOS
• rm block about :focus-visible is experimental

1. Seems like focus works correctly in Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Firefox/102.0
2. It have nice browsers support by https://caniuse.com/?search=focus-visible info

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[chrome-devrel-review-bot]

Hello! This is an automated review by our custom reviewbot. It updates automatically when code or GitHub comments in this pull request are created or updated.

Requested changes

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src/site/content/en/accessible/style-focus/index.md

• This file passed all of our automated Markdown audits.

[chrome-devrel-review-bot]

Hello! This is an automated review by our custom reviewbot. It updates automatically when code or GitHub comments in this pull request are created or updated.

Requested changes

If there are any common problems with the content files you created or modified, they will be listed here.

src/site/content/en/accessible/style-focus/index.md

• This file passed all of our automated Markdown audits.