Only someone using your user profile would have that access. Each Firefox profile is separate from any other on the computer.

As to what is displayed when Firefox is started;

Type about:preferences#general<enter> in the address bar.

There are two settings;

• When Firefox Starts

When the browser is started, what do you want to display? Many of us choose Show My Home Page.

• Home Page

When a new page is opened, what do you want to be displayed?

1. Use Current Page. Use what ever page(s) are open at that time.
2. Use Bookmark
3. Restore To Default. about:home shows a Mozilla home page with tools.

You can use any of these that you wish;

about:home (Firefox default home page), about:newtab (shows the sites most visited), about:blank (a blank page),

or you can enter any webpage or about: page you want.

Crash recovery is not a new feature. However, if you use CCleaner, you may be seeing the crash recovery screen a lot. Its feature to clear session data needs to be updated for the new session history file names and formats used in Firefox 56 and later and until it is, you will get session restore screens at startup (or you can turn off clearing session data in CCleaner).

If you do not want Firefox to save crash recovery data, or if you want Firefox to flush all history (browsing, download, and session history) when it closes, those are options you can set.

You can use "Clear history when Firefox closes" to cleanup any personal data you like. If you clear the browsing history then it won't be possible to reopen pages from the previous session.

• Options/Preferences -> Privacy & Security -> Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

Let the cookies expire when Firefox is closed to make them session cookies instead of using "Clear history when Firefox closes" to clear the cookies.

• Options/Preferences -> Privacy & Security -> "Use custom settings for history" -> Cookies: Keep until: "I close Firefox"

You can create an "Allow" exception to keep specific cookies.

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing "Cookies" will remove all selected cookies including cookies with an "Allow" exception you may want to keep

Firefox will automatically try to restore the tabs and windows from the last session if a crash has occurred or Firefox didn't close properly the previous time. If the session crashes another time then you will get the "Well this is embarrassing" page (about:sessionrestore) the next time you start Firefox. You can set browser.sessionstore.max_resumed_crashes to 0 on the about:config page to get the about:sessionrestore page immediately with the first start after a crash has occurred or the Task Manager was used to close Firefox.

• http://kb.mozillazine.org/browser.sessionstore.max_resumed_crashes

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config