Update: 3/23/18 (FireFox 58.0.2 (64-bit); Dormancy 3.3.0): Dormancy has been "losing" tab content for SOME but not ALL tabs I haven't visited for longer periods (~1 day or more). When this happens, first the tab's title remains but its URL is missing (so the tab can't be reloaded), and eventually its title reverts to "New Tab."
Saves a lot of memory, no major problems with Firefox 58.0.2 (64-bit)/Windows 7 Pro/64. With current version (3.3.0), I recommend leaving "keep active window alive" unchecked. Also, the most memory is saved if I let this inactivate windows, then stop and restart Firefox (with "restore tabs at login" active). I will attempt to provide details on this to the developer in the appropriate forum.
Hibernated tabs get a "data:text/html...xyz</title>" as a tab title (where "xyz" is the last part of the page title - it gets truncated to fit tab width). Their favicon is not removed though - which is a good thing in that it helps you guess what site/page was there before. For some of these tabs, this text replaces their url too, so reloading the tab produces an error.
(some) Tabs with google searches that get hibernated loose their search query part of the URL. The actual URL that was there before the hibernation gets replaced by the domain only part of the URL. Don't know if it is relevant, but my home page is set to Google and is fired on every new tab.
Giving the addon 2 starts for the effort and the idea behind it. The mechanics behind the procedure that fires the tab hibernation seem to work. The code that is executed in order to do the actual tab hibernation though is buggy. I'm confident this will be fixed in time. Keeping the addon disabled for now (in order to be notified of future updated versions so I can give it another spin then).
There seems no change in memory used before and after installing this add-on (checked through task manager) but looks like pages are loading comparatively fast.
Only title of tab is not showing correctly (shown from history of tab), but when opened it by clicking it opens correct page. Is this a bug or is in accordance to warning "EXPERIMENTAL. MAY EAT YOUR SESSION OR DO OTHER BAD THINGS." ?
There is scope to improve this add-on otherwise very good functionality (thearotically)
Has this been tested on FF v7? It doesn't complain when installed but it appears to do absolutely nothing to the memory ... waiting for it to unload all tabs (about 60 of them) leaves the memory completely unchanged (around 450 MB).
1. I don't like the system with check intervals. In my opinion - every tab should have some internal timer, which starts counting time since the tab became inactive. And when that timer reaches extensions.dormancy.TabDormancyAgeMs value - the tab should be put to sleep 2. I use Tree Style Tab and your extension breaks trees, when putting tabs to sleep. Sometimes, they get back to normal trees, when re-activating the tabs but only sometimes... 3. Titles of the hibernated tabs look like this: data:text/html,The actual tab's title, but when they get restored - usually their titles get fixed, but sometimes they do not. 4. Hibernated tabs have crop=center instead of crop=end. 5. Bug 675541 should be marked as dependent to the Bug 675539. This bug is about styling the stalled tabs, I suggest adding opacity: 0.8; to them. 6. Sometimes it wrongly stalls a pretty fresh tab (e.g. I'm sure that the tab was too fresh to be stalled: it was inactive for like 3-5 sec [I just switched from it to another tab] and the Age pref is set to 300000.