This works just fine on non-mobile devices. I have not tested it on mobile yet, but my review is based on my desktop/laptop experience. I have seen questions like "Why does this add-on need the user's username and password?" when pointing to the permissions requested, that ask for all browser and input data. The way this add-on works is it creates a brand new request on your behalf using the data you input, as well as the data on the website. Don't be alarmed about it, it is not storing your data. Some people who write reviews don't know how things work, don't know why certain permissions are requested, and make bad assumptions. Enjoy the app on, at least, non-mobile platforms! :)

Very useful add-on, worked well

At least for what I needed, it worked great! .... Using here over WATERFOX 56.2.7.1 (64-bit) OSx

It'll be better if it support to select a version of Windows when IE's UA is selected, but it doesn't matter that the extension can custom UA string, so I can paste UA string of IE of any version's Windows

Best add-on for Firefox. MOZILLA, HEAR ME OUT ON THIS PLEASE: "If you want to compete against all of the websites and services that may in the future, due to the superpower and monopoly known as google, deny Firefox access to certain web pages and services, automatically integrate this into the browser's main code so that whenever a site states: 'Browser not supported', it will always bypass these issues and switch the user-agent to the browser that the site says it supports. Building transforming code from chromium to gecko quantum will preserve Firefox's unique, powerful, better web rendering engine. That is the future for Firefox, and going to college next year, I will learn much about programming, security and computers, preparing me to advance Mozilla as a strong non-profit organization."

It works fine and I really like the style! It looks great! What I'm not such a fan of is that it's a global thing. I'd like (e.g.) the mobile view only for the tab I click the button on, but this switches for all browser windows. Not sure if that's even possible though.