Is there any Firefox extension similar to Chrome's The Great Suspender?
Basically it suspends tabs that are not actively being used, allowing you to have a lot of tabs without consuming all your memory and CPU processing.
Tab Suspender (memory saver) seems to be a pretty good alternative.
There are several options:
Auto Tab Discard (Compatible with Firefox Quantum)
Use native tab discard method to automatically reduce memory usage of inactive tabs.
One Tab (Compatible with Firefox Quantum)
OneTab - Too many tabs? Convert tabs to a list and reduce browser memory
Dormancy (Compatible with Firefox Quantum) [Experimental]
'Retires' tabs that have gone unused for a while, freeing up that memory. It then restores the tabs to life when accessed.
UnloadTab (Not compatible with Firefox Quantum)
Unload inactive tabs, save resources.
Suspend Tab (Not compatible with Firefox Quantum)
Suspends background old tabs automatically to save memory usage.