I haven't tried a lot of tab unloader add-ons but from the ones i used this is by far the best, the most options, easier to see what tabs is unloaded, and a style that fits nicely into firefox if that is what you want ;)

great add-on to lighten firefox and speed it up

Tab Unloader working just fine with all previous versions of Firefox up to 118 (on Arch Linux).
Usefull settings and default settings, ie: time to auto-unload; visually shows which tabs are un/loaded; don't unload tab that's playing Audio...
Also works fine with Tree Style Tab.

Before opening Firefox, is there some way to tell Firefox to tell "Tab Unloader" to open all tabs unloaded?

Still works. I actually use this only for the option to load a whole bookmark folder unloaded.
Would be great if there were shortcuts like ALT + Click on a link to open it in the background. Context menu item to open link in background unloaded also lacks a keyboard shortcut.

More useful than Auto Tab Discard for me, because Tab Unloader correctly counts the time before automatic tab unloading from the moment the tab was last active / in the foreground before the user switched to a different tab. Auto Tab Discard, in my testing, counts the time since the tab was first opened or last loaded back from the unloaded state, which is quite inconvenient.

For me the best extension of its kind. It has all the features I need, but without any bloat. Simple and clear options dialog. An option to "bypass the cache on restore", like the old "Auto Unload Tab" extension (pre-Quantum), would be really nice. At the moment I use the extension "Update Discarded Tab On Select" for this.

He estado haciendo pruebas y ahora mismo funciona mejor que UnloadTabs, además tiene más opciones y un botón para no tener que dar clic derecho sobre las pestañas cada vez que quieras descargarlas.

This is the only one that work perfectly as a tab hibernator on new Firefox

Thank you Afnan Khan, and good people at Mozilla.
I have not tested this extension yet because I still mainly use a version older than FF57("the Great Regression"), but give it 5 for encouragement. Every user of FF that uses more than 10 tabs in a session, needs an "auto unload tabs" functionality, like we need air.
After I have searched(2018) and read about/viewed screen shots (videos), of extensions that are able to unload(auto) tabs, I find this one to be the closest with the extension:"Auto Unload Tab by def00111" which does not work on FF after v56, but does a superb job on FF before 57, of unloading(auto too) tabs from multiple groups without using much CPU.
Hopefully Afnan Khan did not quit maintaining(or improving) this much needed add-on.
About the loosing of favicons of tabs it seems to be a bug of Firefox ("Most notably, tabs may loose their icons or display as loading. Fixing that is Mozillas job")...see more here: https://bugzilla.mozilla.org/show_bug.cgi?id=1450382
https://bugzilla.mozilla.org/show_bug.cgi?id=1450371

Update reacts and unloads tabs much faster than previous version. "Must-have" extension for my ageing Mac, inclusion of menu item to unload tabs in other windows is welcome addition.

Looks like the CPU usage is within reason now. So, this is the best tab unloader with automatic background unloading I've found.

Excelent

FF 59.0b12 (x64)

- Please, add support for the Tree Style Tab API (for the RMB-context menu on fake tabs).

- Please share your addon on github - to be able to write issues and pool requests.

- some tabs are not restored - its happen on tabs that you open in the background but don't get to before the tab unloads.
I see the same bug on auto-tab-discard addon, so its may be a FF bug

Thank you for your development, this addon fully meet my needs!

Must-Have addon!!

Works correctly on Nightly 59.
Unfortunately, "Auto Unload Tabs" function is so heavy. I anticipate that future improvement.

Great addon! Unloads tabs to the same state as when Firefox is closed and reopened when it is configured to restore last session. Really appreciate that it has context menus on both the tab bar and on web sites and that both can be toggled on and off. Makes it usable when I hide the tab bar and use sidebars that work as replacements. Didn't really work correctly on Firefox 58 but it seems to work on Firefox Nightly 59 and I haven't noticed any issues with it yet!