You could turn on browser.sessionstore.restore_pinned_tabs_on_demand in about:config and then pin the tabs you wanna try to keep. If you ever close them by accident you can recover the lost pinned tabs easily.

Note that you can easily reopen a tab you closed accidentally via Ctrl+Shift+T.

Pinned tabs are a bit harder to close and to override, so you could try to pin these tabs to see if this works any better.

You can find items like "Pin Tab" in the drop-down list that opens if you click the "Page actions" button (3-dot icon at the right end of the location/address bar).
You can right-click an item in the "Page actions" drop-down list to add its button to the location/address bar for easy access.

Hello hogglegg,

Maybe you'd like to do what I did :

Type in the address bar   about:config   and press Enter.
(ignore the warning)

Type in the search bar and look for the preferences :

browser.tabs.warnOnClose

browser.tabs.warnOnCloseOtherTabs

And set their value to   true.

Then close and restart Firefox.

I always get a warning when I'm about to accidentally close one (or all) tabs.

Thank You Eve and Cor-el, I will certainly check these suggestions out. May God Bless You Both! ✝