What does the CCK2 do?

CAPSCheckLoadURI.jsm

Allows pref("capability.policy.default.checkloaduri.enabled", "allAccess"); to work.

CAPSClipboard.jsm
CAPSClipboard-fs.js

Brings back the clipboard security API

CCK2AboutAddonsOverlay.jsm

Fixes the bolding on the about dialog

CCK2AboutDialogOverlay.jsm

Workaround https://bugzilla.mozilla.org/show_bug.cgi?id=1132971
Hide the "Install Add-on From File" menu if xpinstall.enabled is false
Hides the discover pane if xpinstall.enabled is false
Hides the add-on entry if specified in the CCK2 config

CCK2AboutHomeOverlay.jsm

Remove the sync button if Sync is disabled
Remove the Addons button if Sync is disabled
Remove the snippets if snippets are disabled

CCK2AboutSupportOverlay.jsm

Remove the reset Firefox button if disableResetFirefox is set
Remove the safe mode Button if disableSafeMode is set
Remove the box if both are set

CCK2BrowserOverlay.jsm

Modify the browser UI

CCK2FileBlock.jsm

Prevent certain files from being loaded in the browser (browser.xul)

CCK2PreferencesOverlay.jsm

Removes private browsing from the pref UI if it is disabled
Removes Sync from the pref UI if it is diabled
Disables the crash reporter button if crash reporter is disabled
Removed the master password UI if it is disabled
Goes through the hiddenUI list and hides any UI

CCK2.jsm

Sets prefs
disables about
disable in page search providers
hide UI
Bookmarks
Certs