Wow, that's really strange. Either Google messed up in sending that information as the page title, or some kind of password revealing add-on would seem to be inserting it there.

A standard diagnostic for interference for problems created by add-ons is to try Firefox's Safe Mode.

First, I recommend backing up your Firefox settings in case something goes wrong. See Back up and restore information in Firefox profiles. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.)

Next, restart Firefox in Firefox's Safe Mode (Diagnose Firefox issues using Troubleshoot Mode) using

Help > Restart with Add-ons Disabled

In the Safe Mode dialog, do not check any boxes, just click "Continue in Safe Mode."

If your Google pages come up clean (no password in the title bar), I would suspect one of your extensions as the culprit.

Any new insight from this test?

You can delete the places.sqlite file to be sure that all history references are removed.

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox
• https://support.mozilla.org/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file

Use these steps to remove saved (form) data from a drop down list:

1. Click the (empty) input field on the web page to open the drop down list
2. Highlight an entry in the drop down list
3. Press the Delete key (on Mac: Shift+Delete) to remove it.

• http://kb.mozillazine.org/Deleting_autocomplete_entries