I am using firefox 21 but I faced more problems with firefox like many times hang or slow working the browser so I want to install older version means firefox 20 after remove firefox 21 version. Please tell me the procedure of above work.
SnapOverflow
If you have a 32 bit system download: https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/20.0.1/linux-i686/en-US/firefox-20.0.1.tar.bz2
If you have a 64 bit system download: https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/20.0.1/linux-x86_64/en-US/firefox-20.0.1.tar.bz2
If you don't know how to install the files see: How do I install a .tar.gz (or .tar.bz2) file?