How do I uninstall Firefox's latest update but keep the old Firefox?

I dont want Firefox latest update as it has destroyed my history, my bookmarks, and my profile. It has also slowed access to videos and browsing among websites. I can no longer open more than one window at a time for more than a few minutes before Firefox stalls ... just stops working . no crash message... nothing just a single dead window. I must then unplug my computer. I cant even get back to my windows start. My internet provider confirms that I am getting top speed; my tech says that all other single programs like Word and Excel function at lightening speeds but not if they are open in conjunction with an internet website. This problem occurred sometime the week of September 12th when a Firefox update was installed. Now I am prevented from accessing the internet UNLESS I ACCESS THE UPDATE and refigure it. How do I uninstall this update as I need to access videos for a university class and run Word at the same time which is impossible now! dona bretherick