Can I go to Mexico-Tijuana for my H1B visa stamping ?

If you have a valid H-1B visa, you do not need to visit the U.S. Consulate for another H-1B visa. If you still want a visa ( for employer B) , I suggest you return to your homeland and apply there. You need to contact the company's immigration attorney to provide you guidance as to your plans to visit Mexico.

I would NOT recommend this. 1. A new stamp isn't needed ... unless you wish to travel internationally. And, if you wish to travel, then you can apply while on that trip. 2. If the stamps you have in your passport aren't expired ... you don't need new stamps. 3. The US Consular officers in Mexico and Canada are getting 'tired' of people from India going to their post for a 'quick' stamping. Thus, they are starting to put cases into 'administrative processing' .... this could mean that what you thought would only be a 5-7 day trip to Mexico could become a 5-7 WEEK trip. I do NOT recommend doing this.