I've been using Opera GX for quite a while now, and one of my favorite features are the multiple context you can have to organize your tabs into different work spaces without the need for multiple windows. I, however, have a suggestion to take this to the next level.
Opera GX should have a function that allows the user to select multiple tabs and "compact" them. What I mean with it is that the user should be able to create a temporary folder so he can store a setup of multiple tabs easily, being able to close them once they won't be using them for a while whilst also able to reopen them easily with one click. This way, the user won't have to keep multiple tabs open in order to use them later, reducing the demand on disk and memory.
It may seem little at first, but I am sure this would be a feature that would help immensely students, for instance, with their organization, greatly boosting their performance.