Thanks a lot for the review. Actually the idea is really good. I will add it to the feature list. Can't promise how fast will be integrated but I will add it for sure.

Thanks for review. The easiest way to delete everything is just open Bookmark Menu (CTRL + SHIFT + B) and select the SessionSync folder and delete any folder you want from there (or all of them). Assuming that by deleting you really mean to remove them completely, that's the easiest way. Of course you can't really restore them after that. If you think you need them you can just move them elsewhere and they won't be showing anymore in the "Session" Tab

I don't really know what to say. It's true that the addon doesn't do that. But, at the same time it was never really meant to do that. Receiving a negative feedback because the addon doesn't do something I never intended to seems a little bit weird, even if you may consider these features as really important and critical for such an addon. Please have in mind that each particular addon is implemented with a certain set o features, and many new features can be added later or will never be added because they are not in line with the addon vision. That's why there are multiple options out there, because there are many developers that though of implementing similar useful things. Not having something in an addon, doesn't mean it's bad, it may simply not be for you. Thanks for review anyway.

Hi. Thanks for review. I will assume that you are talking about manually saved session and not the one from the auto-save tab. The only reason any blank space might appear after you delete a session is if you ordered them by something else than position.
But then... you say that everything is blank ?! But that can't happen for manually saved session because the addon never ever touch that data automatically so deleting it is out of the question.
Please if you can contact me over email I might be able to fix a solution for the problem. First, if you are talking about saved session you have constant backup of them by Firefox and you can restore everything for a few days. Second, if any bookmark was really deleted trust me... the addon is not at fault. There's simply no way the addon will ever do that under any circumstances. There's nothing like that. You either delete it or it will be forever stored into Bookmark Menu -> Session Sync folder.

Everything you manually store is in Bookmark Menu -> Session Sync folder... so if data is there... the it should be displayed in the addon as well.
If you're talking about the auto-saved session... that I can't do to much about them. But if you talk about bookmarks session... even if there by any strange reason you have an error. Reinstalling the addon will make it work without any problem because the data is there in the bookmarks and it will never be deleted randomly. Why you can't access the links... I never encounter this error and I don't actually understand why it won't be fixed if you close the panel and open it again because each time the data is requested from the bookmarks and even if there's a small error it will be fixed right after opening it again.

Like I said, if you can, please contact me over email (press the feedback button from the addon menu and you will be redirected to send an email), because I belive that the issues should be fixable. Just giving it 3 starts after using it for an year will not help anyone, not me, not probably not other people because the issues seems quite strange and there are thousands of people that constantly delete session and there's no issue like that so I assume there's something very edge case here.

Thanks a lot for the review. I really appreciate it. Assuming that this request keeps coming I'll have to see what I can do about it. Can't promise a fast implementation for it but I will definitely try to look up for a solution because it's clear that it's a feature many user expect. Of course, it will come with a few limitation, like only being able to sync a certain window and not all of them, because a session is stored just as I window and not as a collection of windows and right now it will be kinda impossible to track multiple windows at the same time. I intend to offer an option for this before the end of the year. Thanks again.

Thanks for feedback. Regarding to your question. Can't you actually use the overwrite session feature ? There are a number of reasons why I didn't implement automatic tracking for sessions, because of performance when using the bookmarks as storage as well as because you are free to open as many sessions as possible and not decide for yourself what you want to save or not. I understand that this is a limitation compared to other sessions but this addon is mostly intended for on-demand saving and not really tracking every step. Implementing this feature is not really easy but if I find the time I might try to implement a special option to do so. But just so you know... if you close open tabs, for sure you can loose data from the old session because everything will be constantly replaced. I know for sure that for some users that would not be a good idea, so the only way I can possible implement this is through a special option, and not as default behaviour.
In the meantime... In your case though, if you select the old session and press the Overwrite session button it should behave just as you want? Or is it not ?

Thanks for review and for using the addon. Yes, sadly there are a quite few missing features but in time I hope to close the gap and be able to provide as many options as possible to meet everyone's expectation.

Thank you for using the addon. I know that's a long time requested feature, once I find a good solution to provide all the required features I will definitely add support for Tree Style Tab.

Update 2:
I'll definitely look more into it. And try to fix it. But trust me, unless I can reproduce this myself, it's impossible to know if what change I do are good or not. So I have somehow to find the cause why it is happening first. I'll try maybe to use a really old PC to see if speed can affect it.

Update:
Well... maybe but again. If one of them works for you doesn't really mean one is flawless and the other one has issues. Also like I pointed you, the fact that things are not saved as they should is not something common or directly a bug from this addon. There can be lots of reasons for it (even other extensions at fault that mess with settings or who knows). If there was a chance for me to understand the bug and create the same issue trust me I would have fixed it long ago. I tried on multiple sistems, different configuration, etc, etc... but I had no chance of repeating the bug. If I can't find the issues it's extremely hard to point to an issue in the code. Also, as much as I look over the code there's not something I find wrong with it. It's really strange. So the fact that MySession works in your case doesn't really tell me anything just as with the fact that this extension doesn't somehow works as it was suppose to. There's something else at fault, most probably. I mean...

The way I save bookmarks is like this... If you have 100 tabs.. then I take each one and tell Firefox
- save the first one at the end, when done... I select the next one and save it ... and so on
How this can fail and turn everything into a mess in the bookmarks... god knows... because that's clearly not what I do. So I bet it's something internal to Firefox, just as what Firefox does on the Firefox Mobile side where it randomizes everything in bookmarks like hell. The order I have on Desktop has nothing to do with now it sees that information in the mobile version. From what I notice, it might order them by access time and not by position or whatever it does.

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I'm really sorry that you have this bug, but trust me that's not something common. As much as I wish to fix it there simply nothing I can find wrong with the code. Also the bug seems to happen only for some users so I don't know if it can be related to the speed of the computer or who knows. The only thing I can think of is if somehow Firefox saves randomly some bookmarks although I specifically send the order and save them one after one on purpose. I really have no clue, but probably I will try to create a second check to make sure that everything was saved as it was suppose to and if there was any problem regarding the order to just order them as they should.
I tried with over 100 tabs multiple times, every single time I try to replicate the issue myself I can't simply find it and it's really hard to fix something that only happens in some specific conditions. Not saying that this is not an issue, just point out that it's really hard to find out why it's happening for some users and for others never.

I will try to give another chance to the API. It was suppose to work "out of the box" or that's just what Mozilla says but when I put it on mobile everything was blank. No errors, no issue no nothing, just a blank screen, and I had to cancel mobile support because simply I had no idea what the issue was and/or what to do. But I will try to check again if things work better. Sadly if there is any need to redo the UI for mobile things might not be that straight-forward so I can't really promise anything.

P.S Just in case you were not aware: All your saved sessions (in bookmarks) are still accesiable on Firefox mobile if you look for them in Bookmarks->Menu->SessionSync. I know it's not ideal but at least there something and you can still look up for things if you really need to.

Updated after user answer:

Thanks a lot for the detailed explanation of the issue. I promise that I will go through each one and investigate it thoroughly to find the bug.

Regarding the other 2 issues:
1. The scrollbar is awfully small on purpose, let's just say by design (I thought that a non intrusive scroll bar is better because I expected most people to just use the mouse scroll )... of course, it doesn't have to be like that, it can be stupid small and I totally understand that. I will make sure to add an option to configure it to be just normal. Regarding the interference from the popup with the scrollbar... this one also on purpose because it looked a little out of place to move it near the scrollbar. Not really sure who to approach some things having in mind that there's no real solution to place everything on screen and not affect something else. I will think about it. The fact that the mouse can be glitchy sometimes... I'm afraid that can't be something from be but most probably from the addon popup window (if in the Tab View it doesn't happen then that's for sure)

2. Need to investigate that further, because it seems really weird

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Are you sure they are not just in reverse order ? Depending on certain Firefox setting each user has, tabs can be restored in reverse order or in the normal order (If for example you activated new tabs to be opened next to the current one or similar settings). This is not something I can control myself since each user can affect the order of the tabs. I just simply tell firefox to open all the links no matter how many they are. If there are 1000 tabs I tell Firefox to open all of them in the right order they were saved. I wish there was something wrong with the way the Addon was built but trust me there's really no issue. There can be multiple settings (from other addons or just Firefox settings) that can mess up what I tell the browser to do.
That's why I added the "Reverse restore order" feature in the Options. Please check that one to see if order will be preserved.
The addon knows to open even more than 10000 tabs, but depending on the number you want to open I'm not really sure if Firefox can really handle it (more exactly if the PC hardware can handle it the correct way). The thing is, if there's really a bug in the way Firefox opens 100 tabs when I tell him to do that I can't really do anything about that.

Anyway, I will investigate this again, but there's simply nothing wrong with the addon, I do what I must (I mean.. really... I go through every single tab and request Firefox to open it... it's not like I can't really do it properly), but if tabs are not opened then I probably have to check if there's any limitation regarding what the addon API can do, or if Firefox might miss some messages from the addon and I will try to find some workarounds.

Regarding your request to show the number of tabs next to each session. Yes, sorry about that, I will try to land it in the next update (the feature is planned but I kind forgot about it).

Regarding the rating, please have in consideration that there are extremely few people that really have hundred of tabs opened and restored so even you if are totally right the review might not be in line with most of the users. I really try to improve it constantly and even if I do something wrong I try to fix it right away. Having support from the community it's what drives me to continue to improve it :). Issues are fixable, but sadly bad ratings remain no matter what I do :(. No, I'm not asking to change your review, I just wanted to point out that it may not be a very accurate review for whoever intends to use the addon in the future.