why can't I have access to this page?

Did you look at History settings and use the option to clear out any passwords or history and then close and reopen so it didn't save any passwords or history?

Type about:preferences#security<enter> in the address bar. Note: For Firefox 56+ its; about:preferences#privacy

Under Logins, Turn on Remember Logins. To check the passwords you have listed, press Saved Logins.

Locate that website, then delete or edit the entry.

You can use these steps to remove saved items from an autocomplete 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 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

Note that hovering with the mouse no longer works.