You should keep pinned tiles (tiles with a pin attached), all other are coming from the history and can be replaced at any time.

• https://support.mozilla.org/en-US/kb/customize-items-on-firefox-new-tab-page
• https://support.mozilla.org/en-US/kb/customize-your-new-tab-page

They are pinned!!! They still disappear

Changes made manually on the Firefox Home page are stored in prefs that you can find in about:config, so it is possible that you do not keep these prefs.

• browser.newtabpage.pinned => websites pinned to a tile
• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

In case you use "Clear history when Firefox closes".

• do not clear the "Browsing history"
• Settings -> 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

Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox Title bar, especially if you have multiple windows or Private Browsing windows open to prevent losing tabs in unnoticed windows.

• "3-bar" menu button -> Exit (Power button)
• Windows: File -> Exit
• Mac: Firefox -> Quit Firefox
• Linux: File -> Quit

Thanks for your reply. I don't delete history when Firefox closes. I have enabled synchronising across connected devices so my history and tabs are shared with my phone and my second laptop.

I normally exit Firefox by clicking X on the title bar. I assume from your response that isn't the cause since my settings don't delete history (see attached screenshot)

I have checked browser.newtabpage.pinned and attach the current setting. Is it correct?

Are pinned shortcuts remembered when you aren't signed in to your sync account?

You can possibly set its Sync control pref to false to exclude pinned tabs from Sync.

• about:config => services.sync.prefs.sync.browser.newtabpage.pinned => false
• https://support.mozilla.org/en-US/kb/about-config-editor-firefox