And I suppose, mining from the same computer on different browsers is forbidden?
Yes, the system will disregard requests that come from a different tab/browser on the same computer now, but it will still process the highest single result.
You can mine with multiple devices though and the same IP.
Are that mining withdrawal process automated, or do you process them manually?
It's manual at the moment, there is an automated system that is being tested- it just has to be 100% solid before being released as any glitches could be catastrophic to the coin and allow someone to drain the reserves too quickly.
How long does it normally take to withdrawl from the miner?
At the moment it's ~24 hours.
There will be more airdrops being sent within 24 hours also.