Gmail - interface changes

I recently visited Gmail to read mail and was surprised to find that the appearance of the service has changed! In addition to changes in appearance, the address book in the mail has been changed radically, and a number of new features have been added, such as setting color-coded labels, changing Google Talk options, etc ...

(I was particularly surprised by the advice of Google to disable Firebug, because “Firebug slows down Gmail” )

It is noteworthy that after 4 days everything became as before. I would like to know the opinion habrois about this.
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PS Is it really only one that affected me these changes?