If you want to try these performance improvements (servo, e10s) but keep legacy add-on compatibility (at least for now) I suggest installing firefox 56, disabling auto-updates, and making the following changes/additions in about:config

browser.tabs.remote.autostart true browser.tabs.remote.force-enable true layout.css.servo.enabled true

This way I get to keep my Tree Style Tab, Lastpass, and a few other add-ons that haven't yet been ported to WebExtensions.

Convenient FTP link, since it seems right now the automated installers are jumping between versions 55 and 57: https://ftp.mozilla.org/pub/firefox/releases/56.0b12/