As you wanted to install a new Firefox browser,just create a new profile for new firefox is enough,no need to uninstall and install again.
Step 1- Click Run then type ‘firefox -p’ and press Enter,( you must close all the firefox browser before do this)
Step 2 – Select ‘Creat profile’ and give a name for new Firefox profile (such as firefox 2),then click finish.
Step 3 – It will pop up a window,just delete the old Firefox profile (new1) and uncheck ‘Don’t ask as start up’,then click ‘start firefox’.Now you can get a ‘fresh’ Firefox browser.
Moreover,you can use this method created 2 Firefox Browser;first browser fulfill with plugin and extensions,second one is a fresh firefox.You can use the fresh Firefox to browser website,weblog,forum,etc caused the speed fresh Firefox is faster than Firefox with plugin and extensions.As you need to download or use extensions function ,just switch back to the normal Firefox,all you need just put a check in ‘Don’t ask at start up’,then will pop up a window ask which Firefox profile have to use every time.
I always use this method for my Firefox browser,it quite easy .