passwords and usernames i have for my sites got erased

Did you have them after updating Firefox, or did you lose your passwords as well. If you lost everything you either created a new profile and are in it, or you accidentally/intentionally cleared your history (see picture link). If you cleared your history, the changes are permanent and they are gone.

If you cleared your history, except for bookmarks in backups, you will have to try for

1. Data in an older profile, for most people this would only be if one accidentally created a new profile, such as during a Firefox installation.
2. Your own backups
3. Old password, cookies from Internet Explorer

Use the "Alt" key to temporarily see your toolbars. Use the view menu to display any toolbars that should be displayed, such as the Bookmarks Toolbar.

Check these:

• Do you have bookmarks Ctrl+B (Bookmarks sidebar), if you don't see your own bookmarks but you see those from when you first installed Firefox, you are probably in a new profile, using the Profile Manager could bring up another profile.

• Check your current bookmarkbackups for dates

On current profile, you can check dates, and restore/replace current bookmarks from a backup. "Ctrl+Shift+B" to bring up the Library List, then in the "Import and Backup" menu, choose Restore to see what dates are available. This will tell you the last 11 dates you used your current profile in Fx5 (5 days if Fx3). You can restore if your bookmarks are messed up.

Profile: Find out if there are multiple profiles

type in about:support into the location bar
:Click on "Open containing folder"
:You are now in your current profile
:go up one directory level to "Profiles", where you can see if you have more than one profile directory
:files of interest (check last used/update dates) within profile: places.sqlite file, and within bookmarkbackups folder are .json bookmark backups for dates.

Deleting History/Lost History (Tools -> options -> Privacy), make sure you are not clearing in "Settings for Clearing History" anything but cache. The items you have check-marked there will be cleared at end of session if "Clear history when Firefox closes" is check-marked. If under tools you click on "Clear recent history Ctrl+Shift+Del" you should be asked for how much history to delete {1hr, 2hr, 4hr, today, everything} and what to clear in the details drop-down. Make sure when using the location bar you are displaying both "History and Bookmarks" so the AwesomeBar can look for items from both.

• http://img232.imageshack.us/img232/4928/clearcachew.png

You should be backing your for Firefox profiles, there is not a lot of data and you should be backing up frequently. The is a lot more data for other applications in you Windows user library and you should be backing up data from there as well.

When you backup all of your user data to external hard-drive (500GB to 3TB) your Firefox profiles would be included.

But this is about Firefox. For Firefox a thumb drive would probably suffice to backup one or more profiles.

backing up your Firefox Profiles (the following is all on one line)

xcopy C:\Users\<username>\AppData\Roaming\Mozilla\Firefox\Profiles\*.*   g:\profiles\*.*   /s /d /h /y /c /q  

Profile references:

• http://kb.mozillazine.org/Profile
• http://kb.mozillazine.org/Profile_Manager
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox
• http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox

it looks like i accidentally deleted my passwords, how can i set up a new profile to start all over, I have already tried deleting and re-downloading Firefox.

http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows

Do you mean names and passwords in the Password Manager or do you mean that you are no longer logged on to (remembered by) websites after closing and restarting Firefox?

There is a difference between remembering the name and password in the Password Manager and a "remember me" check box on a web page.
The latter usually involves the creation of a special "remember me" cookie that is stored on your computer and that is send to the server.
If that "remember me" cookie is removed or gets corrupted or is not send to the server then the server won't remember you and you need to sign in once again.

• http://kb.mozillazine.org/Cookies
• http://kb.mozillazine.org/Websites_report_cookies_are_disabled (Other Solutions)

If Firefox doesn't offer to store passwords in the Password Manager then check that you aren't running Firefox in Private Browsing mode.

• https://support.mozilla.com/kb/Private+Browsing