how do i remove the suggested stories of the day popular today, long reads, the latest, etc. on my Firefox home page ?

You can disable them. Here is how https://support.mozilla.org/en-US/kb/sponsor-privacy#w_how-to-disable-the-sponsored-shortcuts-feature

There's just a convenient switch to be flipped in your home customization (the pencil icon in the corner) — the article for this feature is: https://support.mozilla.org/en-US/kb/recommendations-firefox-new-tab#w_i-dont-want-to-see-recommended-stories-on-my-new-tab-page-how-do-i-turn-this-off

these don't work for me. I go into the settings, the little pencil at the bottom of the first page turn off every story etc. but when open a new tab they're there again and the setting is back to turned on.

+1 to jbr's reply above. See also Customize items on your Firefox New Tab page.