I agree with the others- I have been using the free version of Tabs Outliner with Opera for a while, and I love it. I don't want to switch to Chrome because I like Opera's built-in features and how it's not Google, which tracks everything we do and subtly manipulates us with its tailored search results, et cetera. 

I know I would eventually be able to use TO with Opera if it was made open-source... I used to want to pay for the paid version in Opera- but now I don't, because I don't know what I'm paying for. I don't think I'm supporting any of the additions mentioned by TO: "Tags with autocompletion, custom styles, node's icons, multi-select, undo, better and richer notes, better search, real-time backup of all changes, fully synchronized remote editing, mobile access."

Is there an architecture rewrite I should be looking forward to? "... the ongoing architecture rewrite that must hugely improve performance and memory management within the big trees. Future development of this tool depends on your support."

I would give you my money if the license wasn't bound to the Chrome email. Both Firefox and Opera support Chrome extensions; I rarely run into extension problems as an Opera user, but I am unable to grant access to any sort of email, so I cannot buy and use the paid version of Tabs Outliner....However, I have my reservations about doing so especially after reading the above.

I agree that you shouldn't have to give your email to see the price, and that the price is quite steep for this sort of thing. I've paid a max of $10 or so for iOS apps that are full 3D model suites. I'd expect an extension like this, while comprehensive, detailed, and wonderfully user-friendly, to be around $5. Even so, as @parahippocampus said 3 years ago: "Sure, Opera does not have a huge market share, but the kind of people who use a non-mainstream browser are much more likely to be the kind of power user who would pay $20 for a browser extension." I match this description. Perhaps you would get more purchases from non-Chrome users who are grateful. 

Armchair marketing commentary aside, I'll have to move on because the disabled shortcuts are killing me. I think it's an amazing extension though, and would (begrudgingly) buy the paid version if I could.