Spun off from https://bugzilla.mozilla.org/show_bug.cgi?id=1657892#c35; see discussion & profiles in that bug for background.

This is the non-shared-fontlist version of bug 1658207, so will be largely obsolete once the new fontlist is preffed on everywhere, but in the meantime we should do this.

https://hg.mozilla.org/mozilla-central/rev/1f45c61b2fde

Verified fix on 81.0a1 (2020-08-19) on macOS 10.15.6 and the wiki page zooms correctly.

== Change summary for alert #26758 (as of Thu, 20 Aug 2020 10:42:19 GMT) ==

Improvements:

14% perf_reftest_singletons bidi-resolution-1.html linux64-shippable-qr opt e10s stylo 390.81 -> 335.50
14% perf_reftest_singletons bidi-resolution-1.html linux64-shippable opt e10s stylo 351.79 -> 302.45
14% perf_reftest_singletons bidi-resolution-1.html linux64-shippable-qr opt e10s stylo 391.70 -> 336.87

For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=26758

Comment on attachment 9170391 [details]
Bug 1659453 - Accelerate gfxFontFamily::SearchAllFontsForChar by setting up the family charmap. r=lsalzman

ESR Uplift Approval Request

• If this is not a sec:{high,crit} bug, please state case for ESR consideration: This patch has proved very useful in mitigating a significant performance issue documented in bug 1677272
• User impact if declined: Thunderbird esr78 users on macOS Big Sur suffer display delays of several seconds. Perhaps Firefox ESR will also benefit, but have not searched bugzilla for applicable reports.
• Fix Landed on Version: 81
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Patch has been shipped in Firefox releases for several months, and no regressions filed against it.

No alternative has been found to date, other than not updating to Big Sur.

• String or UUID changes made by this patch:

Jonathan, do you have any concerns about taking this in ESR?

(In reply to Ryan VanderMeulen [:RyanVM] from comment #7)

Jonathan, do you have any concerns about taking this in ESR?

No concerns here; it's a simple patch that gives a substantial improvement in some cases, and introduces minimal risk. I'd be in favor of taking it.

Comment on attachment 9170391 [details]
Bug 1659453 - Accelerate gfxFontFamily::SearchAllFontsForChar by setting up the family charmap. r=lsalzman

Thanks for the input. Approved for 78.7esr.

https://hg.mozilla.org/releases/mozilla-esr78/rev/324b0f377893