Very nice idea. But wish for 2 extra features:
(1) White list. Right now we can only choose to ignore all pin tabs or not. For example, I only want to ignore gmail pin. So a white list will be more flexable.
(2) This is more for desktop and I switch between a lot of tabs. However tabs reload the whole page when activating. This become quite painful. It will be nice to have option to choose the "sleep mode" between suspended(eg. just stop/pause script) and clearing completely(the current way).

I set the timer but it doesn't seem to work. I set for 5 minutes but no tabs go to sleep. It only works if I set it for 0 minutes, but then all my tabs are put to sleep immediately and I didn't want that. I'm using Firefox for Ubuntu Linux (latest version 66.0.3).

This addon is really useful for people like me who open a lot of tabs. it really does reduce ram usage.

However there seem to be some issues still lingering:

1. For some reason opening a new tab from either a hyperlink/image/etc... through right-click/scroll-button, will make the new opened tab, completely blank. the name of the tab is still there, but the page cannot be accessed and since the url is also blank, you pretty much can't do anything. This is really annoying and needs to be looked at

2. there are times when my browser is stuck and i can't do anything. The best example i can give is when i turn off the addon while a bunch of tabs are open.
This needs to be adressed as well

3. Could i get more explanation on the whole pinned tabs? how do i do that?

Could you add an option to set a delay for when the tabs go to sleep?