Update: Wow, it's getting better and better!
Features needed:
- more compact list of sessions (see Session Manager)
- save the scroll position of tabs (needs an API change)
- restore the back/forward history of tabs (needs an API change)

Done:
- ability to import sessions from Session Manager (first feature to add, as users won't migrate if they lose their sessions)
- only reload the selected tab of each window (nice workaround to bug 1378647!)
- ability to save only a window instead of all of them (see MySessions for a great GUI for it, but all windows should be saved by default)

Thanks!

It would be nice if I could manually set the location where the sessions are saved.
I'd like to have the sessions saved to my cloud folder so that I can have the sessions synced between computers.

最高

Works with firefox android version 57 which is currently(2017.11.15) beta version available in google play (2017.11.15). To save options in android, you have to edit the option, press save and then 'stop' the add-on restart the add-on by pressing 'use'.

It has becoming my liffe savior at work/home/studies!!

<3 I just fell in love with this Add-on!! <3

ChromeからFirefoxへの移行でChromeのFreshStartと同機能のものを探していてこちらを利用させて頂いています。アドオンとしては特に問題も無く素晴らしいです。
ただ、機能的にChromeのFreshStartのような細かい機能が無いので以下の機能の追加をお願いしたいです。
- 手動で保存する際に、保存するページやウィンドウの選択/非選択機能
- 保存済のセッションの編集機能
　・保存済みセッションから不要なページやウィンドウを選択して削除
　・保存済みのセッションに現在開いているページから追加したいページやウィンドウを選択し追加

tree style tabに対応サンキュー

Simplicity and effectiveness. A little problem with the fonts, I think the encoding, mine are not aliased also for the options page. A great extension nevertheless.

Extension is exactly what I was looking for - simple and single functionality of saving sessions. But it does not remember the options set. I have disabled autosave, still it keeps saving the sessions.

I have on desktop and love it so I'm trying it on android.

I thought I would try this to replace Session Manager, which will likely not work with FF 57. I disabled SM and installed this, saving my session with the toolbar button. When I restarted FF, I only see one tab, which happens to be the first tab in my session. (It's also a pinned tab, if it matters.) The session displayed in the toolbar dropdown has all of my previous tabs, so I'm not sure what's wrong. I did disable the tree-related option in the settings. (I'm using FF 56 still.) Lot of potential here, though!

Update: When I tried loading a session several days later (including after a restart of FF), it did indeed work.

I really like this add-on because I can use it on FF57+ and it's compatible with Tree Style Tabs.
I have to say though currently I find myself rarely really using it besides for saving the one session that i have every few minutes.
Main reason for that is the restore behavior. Like someone else already mentioned, when you restore a session it opens a new window and loads every single tab of the session.
Loading as in actually opening and displaying each webpage.
It would be much better to have it open the tabs "unloaded" like when you initially start FF.

Next thing would be a few more options and functionalities.
- Prompt me for a session to load on start.
- Make sessions more like dynamic savestates, so i can overwrite them. E.g. I have a session 'General'. When I load that the manager should "know" that the session is loaded and later when the window is closed or the session saved it should save the changes that were made during the session was loaded into that same session state.
Right now you can only save a new session with same name but different timestamp.
- Give option to only save current window or a selection of windows to a specified session. So one can work with multiple sessions at the same time.
- Give option to load session to current window or open in new window / attach to current session or open as independently loaded session.
- use standard UI font
- introduce groups
- save and restore per tab history

With all of this it would be perfect (and basically a clone of legacy add-on "Session Manager")
I know it's a lot to ask and some things aren't even possible yet due to Mozilla not releasing the needed API.

It does its job.THANK YOU!

Good job, It works very really well.Thank you!!

Right at the time I was looking for a replacement for OneTab this beauty appears. Thank you very much.