User Agent Switcher is a Firefox add-on that allows you to set a different user agent – Internet Explorer, for instance. This tells sites you are visiting that your browser is of that type, and not a Firefox browser.
Most websites are set up with generic HTML, to work with the many browsers out there and not just with Internet Explorer (for example). Occasionally, you may run across a website that just doesn’t seem to want to let you do useful things like order the company’s products. I had this happen to me a couple of days ago. Thankfully, I already knew about user agent switching and did not get too upset.
This is the first time in a year and a half of my using Ubuntu and Firefox, that I had a problem with Firefox not being accepted. Just in case you ever run into this glitch, though, I have included the link above as one option to handle it.
Happy Ubuntu’ing!