Change UA of Firefox

How to Change UA of Firefox without any Add On
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Yesterday I decided to download Mobile Rediff.
 It is a rediffmail client and can  also backup contacts to its server. 
I want to keep every app that I download for  later use.
 In my Nokia 2730 classic, default browser is Opera Mini.
 So I was  unable to download it as the UA differs.
 Also I need the JAD file to get the  signed app.
 UC Browser is always a better option as it can use phone's UA.
 I had  to download the JAD file, then open it with a text editor to get the URL of the  JAR file.
 I tried to go to rediff's mobile site to download the app.
 But it  showed my phone is not supported.
 And It was not possible to download it in  PC



But I wanted to have the app. 
So I changed the UA of Mozilla Firefox  to 
that of Nokia 5130xm and now I could easily download the app.
So here I  describe how.

• Open Mozilla Firefox, then type about:config in the address bar.

• You will see a warning that this can void your warranty(Firefox has a

     warranty???), click I'll be carefull, I  promise.

• Then you will see a page with lots of strings and values.

• Right click anywhere and select New>String

• Then a box will appear. Enter general.useragent.override

• Click OK and now enter desired UA. You can find a list of UA of various

     browsers in a previous post.

• Now you are done.

• To reset the UA to default, again go to the about:config page.

• In the searchbar, search for general.useragent.override

• Then right click the string and select Reset.

This is extremely useful when a site only opens in a specific browser and you want to open it in firefox