Footer line-height changes between pages

[janbrasna]

Description

Following up from #15788 the same line height issue is present in footer too when navigating between m24-base and non-m24-base pages.

Steps to reproduce

Navigate between https://www.mozilla.org/about/ and https://www.mozilla.org/products/ and observe the spacing change within footer.

Expected result

Consistent baseline values.

Actual result

Screen.Recording.2025-01-05.at.23.27.35.mov

(It would also seem the "Follow @…" headings are different size?)

[janbrasna]

The heading "size" change is actually a negative letter spacing specified only for pages using m24-base:

bedrock/media/css/m24/base.scss

Lines 33 to 40 in 4283006

	h1, h2, h3, h4, h5 {
	color: $m24-color-black;
	font-family: var(--title-font-family);
	font-variant-ligatures: none;
	font-weight: 600;
	letter-spacing: -0.01em;
	line-height: 1.1;
	}

So that one differs from page to page too.

[janbrasna]

I'm also adding a note-to-self to check global components between M24–themed and Fx–themed pages, as currently even the CTAs and Advertising additions change their font between navigation:

Screen.Recording.2025-04-23.at.17.57.47.mov

[janbrasna]

This is resolved with #16156 for M24 vs. non-M24 pages, however still reproduces for Fx-themed pages, that use slightly different type scale.

Screen.Recording.2025-05-02.at.0.29.56.mov