After some months of treetabs missing in the sidebar, it has suddenly reappeared, with all 300+ tabs still in order!
I'm so happy about this uber helpful addon getting back on track!
My donation is meant as a big "Thank You!" as well as an incentive to keep on caring about this georgeous baby.

Definitely the best vertical tab extension. Has so many functions that I could get rid of 4 other extensions and use only this one. There've been no bugs or loss of tree structure. Amazing theme support too...

Great bu buggy...
the tabs all appear in the same group (loss of structure).
Plus various bugs monthn annoying.
And sometimes all the tabs disappear. This morning, I lost everything, it's not acceptable: I give up to find something more reliable.

Easily my favourite extension that allows side tabs, as it allows labelling and grouping of tabs into groups.

The problem I describe below the fold is easily fixed by the declopers' suggested workaround, and hopefully will be fixed soon.

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The extension constantly flashes the entire tab sidebar section white every 2 seconds or so - this only started happening today, but I'm not sure why.

Here's a gif of the behaviour - https://gph.is/g/4gpQ7WE

After restarting Firefox, all tabs previously sorted in many groups are in Ungrouped. All informations about tabs in groups are lost. Sorting tabs into groups has already been specified for add-on. There is no situation for the add-on to lose this information. Add-on has poor session management and is unreliable. It is very frustrating for the user to reorder all tabs into groups again and again...

After some time, about 80% of the pages on other tabs were lost. The plugin has **absolutely unreliable** status information management.

This extension seems to be awesome but unfortunately I can't make it work.

All tabs come back to "Ungrouped" after restarting Firefox and even saving the session previsouly doesn't restore them ok.

The message "Session did not match and will not save! Click here to reload" is appearing too. I'm using Firefox restore session, but checking/unchecking it doesn't seem to help either.

Such a shame, this is everything a tab freak could want (groups, folders, tree structure, load/unload) but without a really strong session management, it makes it hard to trust. There's nothing worst than sorting lots of tabs into groups and folders and tree structures to find out later that you've lost all of that back to a flat structure.

Hope the developer can fix this, it really could be an essential piece of software for those of us who work with lots and lots of tabs.

EDIT: It seems if I check on the "Discard tree structure after browser's restart..." option, click on the reload tree message (and then uncheck the "Discard tree structure after browser's restart..." option again) everything works ok.
Haven't had a single crash or problem since, in any of my profiles (and I have quite a few). So there may be some type of incompatibility with my older extension (tree style tabs).

Awesome extension... I'm donating to the author. Hope he can keep up the good work!!!

Sometimes there is a bug where all the tabs are extinguished.

Дерево с вкладками разлетается... почти всегда(((

Was great, now constantly flashes "Session did not match and will not save. Click here to reload" and automatically reloads the sidebar every second or so. Completely unusable right now. Seems to be a common theme.

EDIT: I do start with previous session. After ticking that option and restarting FF, the sidebar loaded ok. un-checked it, opened a few tabs, restarted again, and all is still good. Back to 4 *.
Will rate 5 if you give an option to not flash the 'tabs saved' text at the bottom. it is always catching my eye and distracting me.

Doesn't work, the tabs list is reloading every second and it's unusable

Edit: author provided a fix for the bug

Just installed this. looks like it will be super-useful. I did spend time clicking on all the menu buttons, but still unclear on:
1) how to set up groups and folders and how they differ from each other.
2) how to color individual tab rows
Is there any type of User Guide anywhere??
Thank you.

1. sometimes add-on is loosing the sorting of tabs and all tabs appears in "ungrupped" tab
2. two time add-on losed open tabs at all
3. almost always add-on restores the closed tab in the wrong place where the tab was closed. Mostly the tab is restored at the beginning of the next group
4. there is a problems with a focusing on tabs when current tab was closed

so.. it's raw

It's the best addon for tab management, in my opinion. It has groups and folders , autosave(Tools=>Open Window Manager=>Autosave) and import/export sessions feature. If one "loses" its groups folders, it is really easy to get them back by loading and merging a previous (working) session into the current one through the autosave feature mentioned above. Previously i have tried Tab Center Redux then TreeStyleTabs + SimpleTabGroups(my previous setup).