For those that really need an earlier version of Firefox, find your system and the Firefox version you want in releases, download and start the install.

• ftp://ftp.mozilla.org/pub/firefox/releases/

When reinstalling Firefox from a download, Firefox must be down once the installation starts. When the installation finishes, don't let the install start firefox for you. Instead end the install and start Firefox in your normal manner, thus preventing creating a new profile which does not have your bookmarks cookies, etc (but your old profile would still be around and would).

Try clearing your Cookies for the affected websites.
Tools > Options -> Privacy - Cookies = Show Cookies button
Enter the domain in the Search bar at the top and all the Cookies for that URL will appear.

Hold the {Ctrl} key while you click on each Cookie in the small window. When that list is all highlighted, click the Remove Cookie button in the lower left. When you are done click Close.

Or you can right-click the page, choose View Page Info > Security > "View Cookies" and delete them there, for each different website as you get to it.