Even though this feature is missing in Firefox, you can get it by installing Paste and Go add-on for Firefox. Once the add-on is installed, you get the right click menu option “Paste and Go” on address bar which works similar to Chrome/Safari browser.
This add-on also enables “Paste and Search” right click menu option on search bar, which lets you paste and search immediately without having to click anything.
Note: This add-on has not been reviewed by Mozilla. You may encounter bugs and issues while using this add-on. I’ve not come across any problems while testing the add-on.
Paste and Go add-on for Firefox