This is good reliable addon for tab unloading; has one NASTY BUG.

A Fatfox with 100s of tabs opened will eat all your RAM and all your SWAP space.
This addon beats the Fatfox till it gives back the systems' resources, so you can still do your main tasks on computer.

Requested permissions very good on privacy also. (No "Access your data for all websites".)

Size of addon is tiny ~23KB, works very fast.

4 requests for improvement:

+) Please let user additionally set custom time for "Suspend After". Now time is constrained to limited options and maximal 1 hour. Need longer custom duration.

+) Please set marks on unloaded tabs, so they are visually distinguishable from loaded tabs.

+) Please give in addon extra short-cut-function to upon activation one-time-only immediately unload all other tabs.

Cheers!

Edit: Has a NASTY BUG!!
Once activating "Disable New Tab Suspender" Addon will not function properly after deactivating this setting.
All already active tabs will not get unloaded, like the Addon would have forgotten about them. Only on new loaded tabs Addon does unloading.