A great idea, needing some work Rated 3 out of 5 stars
What I like:
* Unloaded tabs are dim
* Pinned tabs, and tabs belonging to certain domains can be automatically loaded on opening the browser
* Tabs can be automatically unloaded based on an amount of inactivity time that you choose. (inactivity is based on user interaction, not on anything else that might be going on in the tab)
* it's just such a common-sense feature that belongs in any browser. You should never have to close the browser and re-open it to get it unload tabs.
What I don't like:
* If you "Keep Address Loaded" on a tab, it keeps every tab using the same domain loaded. This can have the perverse effect of actually LOADING a whole bunch of tabs you wanted kept unloaded (and that Firefox alone would never have loaded) just because you wanted a single tab open (e.g. a YouTube video of an hour-long lecture). This is a sure way to crash Firefox within minutes, as it tries to keep all of them open at once.