User-Agent Switcher v0.3.0 
User-Agent Switcher can quickly and easily changes your browser's user-agent. There are 26 popular user-agent strings to choose from!
Important features:
a. Toolbar popup UI provides an easy interface to access 26 user-agents. Clicking on any UA, will change your browser's user-agent after reload.
b. The first row in the panel UI is for mobile user-agents.
c. Second row is for desktop user-agents and third row is for desktop operating systems.
d. The last row in the panel UI is dedicated for the control options including a button to change the UA to its default value. A button to edit the current UA, you can also use it to copy the current UA to the clipboard. Moreover, you can specify a particular URL or domain so that UA is only applied to that URL or domain (read FAQ for detailed description)
e. There is also a status-bar in the panel to show the current UA and other info as you move the mouse within the popup UI.
f. Default UAs can be modified from the toolbar panel UI (v.0.1.4)
Note 1: to report bugs, please visit add-on's homepage and fill the bug report form.
Note 2: in order to use custom user-agent strings, please use my other addon, Custom UserAgent String
Review on YouTube: https://www.youtube.com/watch?v=BaJx1HT21QU