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(For example, to close and restart Opera I might have to consider 100+ tabs, where I rarely have more than two or three Fox tabs open at any time. Or I can simulate a new, first-time visitor to my page using Firefox by doing a global delete of all the passwords and cookies and etc, and the only price is that Tea has to type in her Storage Forum password next time she comes here. If I did the same thing in Seamonkey or Opera, I'd have a heap of work to do (or else have to buggerise about with saving and restoring backup user files).
Opera: {Tools} {Delete Private Data} click [Delete] ... done.