I have a new laptop with AMD and win 8 but when I use firefox it keeps crashing. how can I download the previous version? I was told by other users that the previous version doesn't cause this issue.
Check out the "I still want to downgrade" section of this article: Install an older version of Firefox.
You can install Firefox 18.0.2 over Firefox 19.0 without doing an uninstall first.
Firefox 19.0.1 is released to address this issue for Windows 8.