Version 66.0beta, first offered to Beta channel users on January 29, 2019
Increased content processes to 8
Added capability to search through open tabs from the tab overflow menu
New backend for the storage.local WebExtensions API, providing I/O performance improvements when the extension updates a small subset of the stored data
WebExtension keyboard shortcuts can now be managed or overridden from about:addons
Improved scrolling behavior: Firefox will now attempt to keep content from jumping around while a page is loading by supporting scroll anchoring
New about:privatebrowsing with search
Basic macOS touchbar support
A certificate error page now notifies the user of the name of the certificate issuer that breaks HTTPs connections on intercepted connections to help troubleshooting possible anti-virus software issues.
Fixed an performance issue some Linux users experienced with the Downloads panel (bug 1517101).