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If you are terminated for poor performance, you will be eligible for benefits unless your employer can argue that you intentionally failed to improve your performance or were intentionally making mistakes. That would be incredibly hard to prove, and the argument is rarely accepted by the EDD.
If you quit, that poses two problems. First, quitting will disqualify you from benefits unless you can prove that no person reasonably desirous of remaining employed would have done so under the circumstances. That is very, very difficult to prove. The second problem is that if you are quitting because of a medical problem, the EDD may disqualify you on the ground that you are physically unable to work a new job. So, you would need to walk the fine line of arguing that you are physically unable to do this one job but not disabled from performing other work.
In general, one should never quit in anticipation of collecting unemployment benefits. It's possible to get approved by the odds are stacked against you. The far better course of action is to start looking for new work now and only quit once you've secured another offer. Unemployment will never pay you as much as your job, so this is the more financially practical option. Also, studies have shown that it is easier to find a job when you are already employed. It has something to do with employers wanting to hire people who are perceived to be "in demand."
So, if it were me in this situation, I would start looking for another job right now. If you are fired before you find other employment, at least you know you'll be eligible for benefits. If you are not fired, you will be able to seamlessly transition to the new, hopefully much better job.
I hope that you find this information helpful. Please do not hesitate to let me know if you have any questions or concerns regarding the above and I will be more than happy to assist you further.
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