For the add-on sdk we need to be able to pin and unpin a tab

I'm not sure that we want to add this level of complexity to our tab UI on mobile. More generally, we should come up with a way to cope with the fact that the add-on sdk was designed with the desktop UI in mind, but that we're never going to have the same set of UI features as desktop. I think we should have a way of indicating that certain APIs aren't available for mobile devices, and log that to the error console. This won't make all add-on sdk add-ons automagically work across desktop and mobile, but I'd argue that add-ons using lots of tab-heavy APIs aren't really designed for mobile anyway.

Margeret, Mark, I do agree that UI on mobile is and should be different and not every feature from desktop would make sense. However there maybe operations that may not necessary look and feel the same but would serve the same need if it makes sense. For example pinning a tab may not necessary create pinned tab in the tab bar on fennec, instead it may just add a button to the start page so users have a quick access maybe something else. Current situation on SDK side is, when user tries to pin / unpin tab we just log a warning saying it's not supported on fennec. I would prefer something better, but if we think there's logical operations that we could call pin / unpin we should just close this as won't fix.

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