How do you get Firefox to show unloaded tabs with zZZ like in the picture? Is it some plugin or some config?

It’s an extension called Auto Tab Discard

Wow! I just logged in here to check for responses, and found all these helpful and useful replies! Thank you all, you are great!

I also use auto tab discard. This is the only tab to which it prepends a z.

I use the "Auto Tab Discard" Addon which can be configured to do this.

There might be a config for it, but I use a plugin called auto tab discard. Very configurable. Saves ram too

Autotabdiscard plugin

https://addons.mozilla.org/en-US/firefox/addon/auto-tab-discard/

https://addons.mozilla.org/en-US/firefox/addon/auto-tab-discard/

There's a plugin called auto discard. I've used it before but it can cause certain issues with other plugins like simple tabs (it kept duplicating tabs because of the zzzs in front of the name)

.auto discard