I believe you want just 30.0 as I think the ones that end with b# are beta versions. Can someone please confirm?

EDIT: This support post seems to indicate the previous statement of mine is correct.

Download Firefox Full Installer All languages {web link}

What specific reasons do you have that you want to downgrade to Firefox 30?

Old Firefox versions have known security vulnerabilities and you expose yourself to security risks by using them. It is important to use the latest Firefox version to get all security fixes.

• https://www.mozilla.org/security/known-vulnerabilities/firefox.html

Firefox 31.0 disables Norton toolbar, which I use extensively. Until Norton updates the toolbar to accommodate the changes in Firefox, I must use an older version of Firefox.

http://community.norton.com/t5/Product-Update-Announcements/Firefox-31-Support-for-Norton-Toolbar/ba-p/1155994

These patches do not include one for my software package. I was finaly able to find the correct link to rollback to Firefox 30.0 until Norton gets a patch delivered for my software package.

If your Norton software is not mentioned in http://community.norton.com/t5/Product-Update-Announcements/Firefox-31-Support-for-Norton-Toolbar/ba-p/1155994 then they may not support it especially if it is a old one.

This is all they support We have released a Firefox 31 compatibility patch for Norton Internet Security 21.4 and Norton 360 21.4 which is available via LiveUpdate. The patch is also available for the Norton 2013, Norton 2012 and Norton Identity Safe standalone products. The Patch for Comcast Norton Security Suite will be releasing shortly.