Hi, information on how to remove history etc., from Firefox is in Delete browsing, search and download history on Firefox. However, if you wish to remove Outlook history, you may need to look in the Outlook settings or get help from Microsoft, which is outside the scope of Mozilla Support.

If your question is resolved by this or another answer, please take a minute to let us know. Thank you.

To see whether this is caused by Firefox's form autocomplete feature, you can turn that off in the Privacy options. That will not delete old information but will let you test whether saved form information is the problem, or whether it is something else.

To modify that setting, open

"3-bar" menu button (or Tools menu) > Options > Privacy

If the selector says "Firefox will: Remember history", change it to "Firefox will: Use custom settings for history" and then uncheck the box for "Remember form and search history"

To make sure it's a clean test, please don't change any other settings just yet.

If you reload Outlook (mail.live.com) using Ctrl+r and try again, do you still get suggestions?

If not, it's a form history issue.

If so, those probably are part of the design of the website.

Do you mean saved form data?

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 with the mouse or cursor Down key
   do not click the mouse or press the Enter key
3. press the Delete key (on Mac: Shift+Delete) to delete the highlighted entry

You can also clear the "Form and Search history" via Clear Recent history

• https://support.mozilla.org/kb/remove-recent-browsing-search-and-download-history

• Clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, passwords, and other website specific data.
• Clearing Cookies will remove all specified (selected) cookies including cookies with an allow exception that you want to keep.