14 DAY TRIAL // Ubuntu developers have finally decided to drop the support for Unity Integration for Firefox, Unity Websites Integration, and Ubuntu Online Accounts extension, and they have been removed from Ubuntu 15.04 and Ubuntu 14.04 LTS.
Mozilla has big plans for the Firefox add-ons, and they will have to be signed. From the looks of it, Canonical has no intention of going through the process, and they have removed these components entirely. We rarely get Ubuntu updates that just remove packages from the distro, and it's probably the first time for the Ubuntu 15.04 cycle.
"USN-2743-1 fixed vulnerabilities in Firefox. Future Firefox updates will require all addons be signed and unity-firefox-extension, webapps-greasemonkey and webaccounts-browser-extension will not go through the signing process. Because these addons currently break search engine installations (LP: #1069793), this update permanently disables the addons by removing them from the system. We apologize for any inconvenience," write developesrs in the security notice.
The packages will be removed when you start the updating process, and you won't be able to find them in the Firefox add-ons any longer. This should not be a big problem for Ubuntu and Firefox users, and it's more like a curiosity. Interestingly enough, developers were talking a while back to get these packages signed, but it looks like it's been decided against that.
You don't need to reboot the computer, just to restart Firefox.