Yes, there's still an option to enable the menu bar in Quantum. To enable it, click on the <img src="https://prod-cdn.sumo.mozilla.net/uploads/gallery/images/2017-10-22-15-37-15-18c775.png"/> menu button in the upper-right, and choose "customize". Open the "toolbars" dropdown in the lower-left, and select "menu bar". Add-on compatibility is going to depend on the specific addon; you can search for compatible addons on the addons site. This spreadsheet is alsy pretty helpful: https://docs.google.com/spreadsheets/d/1TFcEXMcKrwoIAECIVyBU0GPoSmRqZ7A0VBvqeKYVSww/edit#gid=195613107 , although it isn't created or verified by Mozilla. If you have concerns about upgrading, you can also make a backup copy of your profile folder, which would allow you to downgrade later if you wanted to do that. [[Back up and restore information in Firefox profiles|This article]] has instructions on how to do that. Finally, if you're going to remain on an older version, you should switch to Firefox ESR, which has security fixes that aren't included in 56. Hope that helps!