Add ::-webkit-scrollbar changes to Firefox 155 and 156 release notes

[pepelsbey]

Description

Adds a note for ::-webkit-scrollbar:

• Firefox 155: support being limited to a pref-controlled site list
• Firefox 156: being reported as unsupported in @supports conditions

Motivation

Firefox 153 started reporting ::-webkit-scrollbar as supported, and these two changes walk that back.

Additional details

• Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=2061547
• Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=2062782

Related issues and pull requests

• Project [CSS] Restrict ::-webkit-scrollbar support to a pref-controlled site list instead of enabling it for all sites #45303
• Project [CSS] Stop claiming support for ::-webkit-scrollbar in @supports conditions #45432
• BCD Updates for Firefox 155 beta browser-compat-data#30265

[github-actions]

Preview URLs (2 pages)

• /en-US/docs/Mozilla/Firefox/Releases/155
• /en-US/docs/Mozilla/Firefox/Releases/156

Flaws (1)

Note! 1 document with no flaws that don't need to be listed. 🎉

Found an unexpected or unresolvable flaw? Please report it here.

URL: /en-US/docs/Mozilla/Firefox/Releases/155
Title: Firefox 155 release notes for developers (Stable)
Flaw count: 1

• macros:
  • Macro domxref produces link /en-US/docs/Web/API/WebTransport/draining which doesn't resolve

External URLs (2)

URL: /en-US/docs/Mozilla/Firefox/Releases/155
Title: Firefox 155 release notes for developers (Stable)

• https://bugzil.la/2061547 (1 time) (Note! This may be a new URL 👀)

---

URL: /en-US/docs/Mozilla/Firefox/Releases/156
Title: Firefox 156 release notes for developers (Beta)

• https://bugzil.la/2062782 (1 time) (Note! This may be a new URL 👀)