In older FireFox(FF as follows) than 57 (ver <=56), "Session Manager"(S-M as follows) did a great job.
But in FF ver 57, S-M ended its life, due to the FF's change, cut off "XUL", which used in S-M, and moved to "Web extension".
This TSM seems an good "ALTERNATIVE" of S-M "JUST" for *FF 57*, for me.
TSM is *NOT* a successor of S-M. Different developer makes TSM than S-M. Words of "Session Manger" in TSM made me confusing, for the 1st time. If its name was "TAB MANAGER", might not be confusing for me.
You don't have to take risk to move from S-M to TSM, if you are still using older FF(ver <=56) or PaleMoon, which still has XUL, which is cut off in FF57. (I still use S-M on PaleMoon)
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Following issue was fixed in TSM 1.6.1, using "tab lazy load" option. (FF ver 57.0.1 x64)
Good job! (2star -> 4star)
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at TSM ver: 1.5.0, FFver: 57.0 x64.
"Open" with 100-200 tabs with 4 windows saved, only 1 window opens and 15-20 tabs only resotred.
With or without Tree-Style-Tab. Even in case of tabs with only http/https-style, this occures.
Exporting sessions from this extension, 4 windows and 100-200 tabs seems all saved in the exported file, instead.
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Excellent add-on that has been working well without any issues.

Now that the "Lazy tab loading" option was added it is, as far as I'm concerned, perfect. Thank you so much!

I love the lazy load feature, very nice when dealing with may tabs.

One feature I'd like to see is the option of opening the group in a new window or the current window on a case by case basis. Instead of a single setting in settings, perhaps the use of the cntl key with open would open in new window and without it opens in current window.

Works great for me. Importing .sessions files from Session Manager worked just fine. Will it be possible soon to save the tabs from a single window, not just all open windows? That would greatly increase its usefulness.

Thanks for adding the lazy loading of tabs. Now I can load my 200+ tab session and all the tabs with their names and icons appear, but they don't load until I click on them. Great job. :)

Usefull

Some people can say, use CTRL + SHIFT + T, But I can't save a session about last month this way and control what page I will open.

Best session manager for FF57 so far.
Keep it up.

I've been testing it for two weeks and it works fine.

can be better if can choose to save individual of windows or tabs as session.

Does what it says on the tin. The new update gives export options, so it's even better.

It is the best for now. Session manager was even better but the important things are:

it is open source;
it can import sessions saved by session manager.

In fact too many times I had to lose all my sessions after moving to a new "session manager" addon.

My question is, what for is the permission for downloading files and READ AND MODIFY download history, on top of that, required. That's sneaky and suspicious.
Yeah... That simultaneous loading of all tabs is a disaster...
I'd also vote for a "saved sessions list compact view" option. Like one-two text lines without much space-eating decorations.
Anyway, thank you for active development and support for Tree Style Tabbar! Your addon is indispensable, irreplaceable and a kind of a savior these days!

I had to get this extension as a replacement for "Session Manager" as the new Firefox doesn't support that one anymore. It's a 5 star program and I absolutely hate giving anything less than five stars...but the only reason why I have is because for work I have tabs open to local html files I created myself, and every time I restore my tabs with this extension it only opens up web pages from the actual web and never opens up my local html files that I need which makes me have to go and open them up one by one. I could do it myself, but I got this extension to keep from having to take time to do that so I don't mix them up and can start working right away. Also, it doesn't ever open all the tabs when there is more than one window saved, usually meaning I have to open up all the tabs myself in the second window as well. Hopefully it can get updated soon. It's DEFINITELY much faster than Session Manager, but I need it to save and open all the tabs ^_^

56まで使えたアドオンFEBEのように、アドオンの設定やテーマの画像、ブックマークデータなど全てのデータを一括バックアップできるようになると、Firefoxを再インストールしたり、新しく使う際にとても助かります。
お手数ですが、ご検討よろしくお願いいたします。