Can you be fired for writing on #twitter? Generally no

Legally anyone can be fired at any time for any reason -- but if there is no good reason for the termination the former employee has to be given severance (which usually is about one month's salary for each month worked).

But can writing on twitter amount to a good reason to terminate?

Generally not. A good reason to terminate (legally called 'just cause') has to destroy the basis of the employment relationship. Even wasting time by tweeting at work is not significant enough to justify termination.

Now tweeting trade secrets or saying "my boss is a pig and he lives at [insert home address]" is probably enough to justify termination.

But usually tweeting at work is not a firing offence!