Freshly Opened Salsa Bubbling and Taste Bad?

When I was learning how to can & preserve foods, I was taught that anything made with tomatoes is acidic and that food poisoning like botulism would not grow in an acidic medium, but that any fruit, tomatoes included, can ferment. The bubbling you describe sounds like fermentation, and probably means that the product you purchased was not properly sealed, some yeast spores got in and the thing fermented. One of the major reasons people who can will put by tomato preparations or fruit like peaches or pears is that the worst that can happen if you don't get a good seal is fermentation or possibly some mold due to the acidic environment. This is relatively harmless. With non-acidic foods like green beans or with meats, you can get botulism, which is deadly.

Your bubbling salsa is probably not very tasty and you wouldn't want to eat it. But the little bit you did eat to test it won't hurt you. Just call the manufacturer and let them know the lot number if available, and where you bought it. They'll give you your money back and probably some coupons besides. Chalk it up to experience.

They must not have gotten a good seal on the jar.

I would definitely call the company not just to get a coupon for a new one but so that they know this happened. There's always a chance that this could have happened to an entire batch that they did. In this case you could be helping to have it recalled to protect others' from becoming ill. ??

Definitely, definitely, do NOT eat it.