I don’t see how that could cause security issues, but I’ll just trust you on that. The issue still remains with pinned tabs, however.
Indeed that may not be the intended purpose of the API, but many users (including myself) want the ability to manage groups of tabs in a way that is better than using multiple windows.
That’s why there’s so many Panorama/Tab Groups extensions available, with many tens of thousands of users.
Using tabs.hide/show is how the extensions currently accomplish tab grouping. It’s a very reasonable approach that works well, and it doesn’t require Firefox to create a new API.
As far as I can tell, there is no benefit to the restriction on pinned tabs: users want the ability to do it, and it’s always possible for individual extensions to avoid hiding pinned tabs (if they choose to do so).
So it is strictly more powerful to allow for hiding pinned tabs, with no downsides.
No, they are tabs that I will need eventually, but right now I might not need them, and so I want them hidden.
As I explained, I have various tabs pinned so they are easily available, but when I am in Work mode I don’t want to see them (because they are distracting).
Right now my two options are to give up and be distracted (bad for work productivity), or to unpin the tabs (which then causes them to get jumbled up with a bunch of other less important tabs, making them harder to find and making it possible to “lose” them).
Using multiple windows is not great either, I would really prefer to keep everything in one window. That’s exactly what the “Simple Tab Groups” extension does. It works very well for what I need, except for the inability to hide pinned tabs.