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

It changes favicons in bookmark to a blank icon with a yellow dot. And the worst is it can't rollback to the original one, force refresh don't work.

Does what it says on the tin. Seems to be the only unloading extension out there that does it on a timer.
Would like an option to disable the recently-added favicon replacing though - the pink blotches are unsightly and, for those who already have styling set up around unloaded tabs, unnecessary. The extension also fails to retrieve favicons of unloaded tabs after a browser restart / session restore, so you end up with a bunch of "default" icons with pink circles on them.
Would also be nice if it integrated with Tree Style Tab, so its menu options show up on the side tabs as well.

Sometimes it can't load unloaded tab giving New Tab

Great addon. Sadly the developer never answers the feedback sent to the mail provided.

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

Useful addon to reduce memory usage. Also I can avoid some web sites keeping watching my access.
One inconvenience: Favicons of unloaded tabs are lost in restarted Firefox.

I really like it, it's very useful. But the tab context menu don't work with Tree Style Tab. Please fix that. Thanks

Please auto white-listed web page with changed form.

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

There should be options such as "Don't suspend tabs playing video", "Don't suspend pinned tabs", "Don't suspend tabs with a form unsend". These there would be enough actually.

Почему у большинства выгруженных вкладок не отображаются иконки?

had no effect for me. obviously no working bulk unload extension exists :-(

Work on FF58 :)

Does not work. Looking at about:memory, after "unloading" a tab, I can still see it in memory.

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

Suspende abas somente de vez enquando.

it's ok, but can we get "keep tab loaded" or "keep this site loaded" option?

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!

Exactly what I'm looking for, but it's not totally working. When I choose Unload Other Tabs, only some of them are unloaded, the rest are unaffected.

It doesn't work. It did when I first started using it, and even then it gave no indication of whether or not a tab was loaded. The problem has persisted through the last update, too, so I'm not sure what's going on.