Add a feature like Opera’s Workspaces. These are like virtual desktops but for your browser. You create a “workspace” and can open tabs in it, then you can create a different workspace and create another set of tabs in it and can switch back and forth between the workspaces. New tabs are automatically added to the active workspace.
I regularly have 50+ tabs open when browsing. An (optional) Workspace feature would allow you to group the tabs into logical groupings based on task/function. Many times I have tabs open that are not relevant to what I am doing at the moment. I might not return to them for days or weeks but I keep them there because I do intend (hope) to return to them. Meanwhile they are cluttering up my browser.
Ideally this would probably be combined with a feature where those tabs in non-active workspaces are sleeping or otherwise using reduced resources