I'm fairly sure Opera introduced it first.
replyYes, well, kind of. Opera had Multiple Document Interface (MDI) which was actually (back then) far more flexible than tabs. But yes, Opera was first with MDI, and also I suppose the first web browser for the smartphone.
replyYes. Opera (original, not what is called Opera now) introduced tabs first. I believe in the 5.0 version with presto engine.
replyNo, because Opera and SimulBrowse had it years before Firefox even existed
replyYeah, I remember.
replyI also remember it automatically blocking popup ads. That was a huge deal.