DO not need to go back. Is there a folder on the Desktop called OldFirefoxData ? if not ok... Firefox found corruption in your Profile and made another one. The data is still there in your old Profile. Check to see if 2 Profiles :

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data Find the one with the oldest date.

you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem. Never work with original files.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

If need help with the files come back.

As for the email account you will need to expand on what email you are using if Thunderbird : https://support.mozilla.org/en-US/products/thunderbird

Going back and forth will only cause more data lose, best to deal with it now.

Please let us know if this solved your issue or if need further assistance.

If you still want to go back,

First, Type about:preferences#advanced<enter> in the address bar. Under Advanced, Select Update.

[v56+] Type about:preferences#general<enter> in the address bar. Select Update.

Select Never Check For Updates.

Also turn off Use a background service to install updates <Windows Only>

Install Older Version Of Firefox {web link} Be sure to read everything here.

If you still want to downgrade, look under; I still want to downgrade. Click the Directory of other versions and languages link. Look for the directory of the version that you want. But, remember that old versions may have security issues.

You should also check out Firefox; Extended Support Release {web link} ESR Notes System Requirements

Is today your first day with Firefox 57? Due to interface changes, your Bookmarks may be hidden or look disorganized. You may first want to turn on the Bookmarks Toolbar or add the new Bookmarks Menu toolbar button, whichever you are used to using.

Bookmarks Toolbar

Use any one of these methods to show the toolbar list:

• right-click (on Mac Ctrl+click) a blank spot on the tab bar (or the "+" button)
• (menu bar) View > Toolbars
  On Windows, tap the Alt key to activate the menu bar temporarily.
• in Customize mode > Show/Hide Toolbars (see: Customize Firefox controls, buttons and toolbars)

Then click Bookmarks Toolbar to display the bar.

Bookmarks Menu Button

The new bookmarks menu button () should work the same way as the old bookmarks menu button (), which was the "right-half" of the inseparable star+book duo.

To add that button, either:

(A) Use the Customize panel (Customize Firefox controls, buttons and toolbars) to drag the icon to the desired spot on the toolbar

(B) Use the method from Bookmarks in Firefox - section entitled: How do I add the Bookmarks Menu button to the toolbar?

• Click the "Library" button:
• Click "Bookmarks"
• Click "Bookmarking Tools"
• Click "Add Bookmarks Menu to Toolbar"