Define custom User-agent header in the HTTP request?

Question

I would like to get a glimpse of web-sites created for iPhone devices. In order to be able to view those sites I have to modify the User-agent header in the HTTP request that my browser sends. That way I can trick the web-server into believing that my browser is an iPhone browser, and then the web-server would send my the iPhone version of the web-site.

So, how can I modify the User-agent header that my browser sends in each HTTP request. Maybe there is an Firefox plug-in that allows modifying request headers? Also, I think I heard that Safari allows that somehow....

Answer 1

Yeah you can do this with Modify Headers add-on for Firefox.

Answer 2

You can try the user-agent switcher plugin.

Answer 3

First, there's the following plugin: https://addons.mozilla.org/en-US/firefox/addon/59/

Also, there's Firefox configuration: type "about:config" as URL in Firefox, find general.useragent.* properties there.