Revert "Revert "For mozcentral use Firefox color theme instead of sys…

…tem theme." since -moz-toolbar-prefers-color-scheme was removed"

This reverts commit aae8a21.

Merge pull request mozilla#14387 from timvandermeij/test-utils

Modernize the test utilities

Merge pull request mozilla#14096 from Snuffleupagus/spreadMode-preRender

Pre-render *one* additional page when spreadModes are enabled

Merge pull request mozilla#13790 from Snuffleupagus/update-packages

Update packages and translations

Merge pull request mozilla#13463 from mozilla/dependabot/npm_and_yarn…

…/ws-7.4.6

Bump ws from 7.4.5 to 7.4.6

Merge pull request mozilla#13172 from Snuffleupagus/cleanup-keepFonts

[api-minor] Add an option, in `PDFDocumentProxy.cleanup`, to allow fonts to remain attached to the DOM

Merge pull request mozilla#12897 from calixteman/12895

JS - Fix mouse event names

Merge pull request mozilla#12321 from Snuffleupagus/BaseViewer-valida…

…te-viewer-option

Ensure that the `viewer` property, on `BaseViewer`-instances, is a valid div-element (issue 12320)

Merge pull request mozilla#11947 from Snuffleupagus/GlobalImageCache-…

…assert-not-inline

Ensure that that we don't attempt to cache *inline* images in the `GlobalImageCache` (PR 11912 follow-up)

Merge pull request mozilla#11716 from Snuffleupagus/private-PDFPagePr…

…oxy-pageIndex

[api-minor] Change the pageIndex, on `PDFPageProxy` instances, to a private property