[SamDc73]

But there were already extensions for that, which is a better approach than Firefox developing a feature only a small subset of people will use1.

[boomboomsubban]

For years every Firefox discussion I saw would have some person saying "why are they wasting their time on X? I won't use it til they have vertical tabs" with scores of upvotes.

This perfectly encapsulates the Mozilla position. Every possible move makes people complain.

[cpuguy83]

Hard disagree. The extensions were terrible, at least for what I want, and probably can't integrate with the UI in the same way.