Left french onion soup out all night, still safe?

My answer depends on if you had put the lids on, if the soup was really hot and you put the lid on--you made canned soup.
If the lid was not on some nasties from the air just might have found a nice place to live.

I have never had food poisoning, but have spoken to people that have, and they say it makes you think you're dying. It's really bad...So when I pull a bone-headed error, I ask myself if the price of ingredients is worth a possible hospital visit and suffering several days of agony. The answer is always "NO"! (I once threw out an entire slow-cooked beef roast I forgot was cooling - $14) No food is worth your health - please throw it out.

Microbiologist here. Throw it out. We store bacterial samples at -80 and they grow just fine when we thaw the little buggers out. even boiling it at this point, would kill the bacteria, but maybe not inactivate the toxins they've produced in the meantime.

I agree with all the advice to toss it. French onion soup isn't a significant investment in either time or money. For future reference, when cooling anything, you have 2 hours to get it to 70 degrees or below, then another 4 hours to reduce it to 40 degrees or lower. At the 2-hour-70-degree mark, the food can be refrigerated, but if liquid, should still be stirred every 30 minutes or so.

My main concern, though, is this: why are you freezing a high-liquid food in glass jars?

Toss it, I implore you. High protein, high water, relatively low acid and salt, a temperature above 40* for probably far too long is a recipe for bacterial growth. Broth is used in petri dishes to grow cultures, and food poisoning is no fun at all.

I have a feeling I am going against the current here, but I would freeze and eat. If it's most likely ok (which, sounding like you made it late in the day/evening and froze the next morning it probably is), I would take a chance. I take the same approach to raw eggs. That being said, we have no very young, very old or very immune-compromised folks in our house. I think it's all about your level of risk tolerance. Or the consequences of getting it wrong, i.e., if you're planning on feeding your boss or her royal majesty the Queen of England or your mom, you may want to reassess....

A question: Is the base a meat broth or veggie broth?

Skenny89 is correct. Freezing does not destroy bacteria or their toxins. That's a common misconception. I am a former microbiologist.

I would toss it. Unfortunately, it sat out too long at a temp conducive for bacteria and toxins. Some dangerous toxins are not killed by freezing or reheating to boiling temp. The soup could be fine, but you are taking a chance that is just not worth it.

I would toss them.

If I made anything that needs to be placed in fridge or freezer after cooking and to help me remember, I always use a timer set for 15 minutes. If the items are not cool enough, I reset for another 15 minutes.

as somebody who ended up in the hospital with a kidney infection/stone from food poisoning when i ate soup that had been out, i would say toss it. freezing only renders bacteria inactive, inhibiting it to continue growing. freezing does not kill bacteria, this is why when scientist find frozen samples in siberia they can still bring it back from suspension in a lab.

Freezing the soup probably won't work if it really did go bad. But, honestly, I've made the same mistake before and happily refrigerated and later ate the soup with no bad consequences. It all depends on your personal threshold for food safety. Personally, I'd freeze it and eat it, but I'd probably try it myself before serving it to guests. Other people would likely choose to toss it. It depends on how afraid you are of food poisoning.