Said about Chameleon WebExtension as an alternative
Chameleon is a very good add on. It has many options and the GUI is easy to use. It is open source and therefore tranpsarent. A very good feature as well is it allows a fake / random user agent to be "fixed"--and not rotated around each time or a set intervals. A lot of user agent , like Random User Agent do "not" allow you to set a fixed fake user agent--and rotating changing user agents can be less unique and stand out. It does what is sais very well.