Personally, though it could happen to anyone, I think OP shares at least some of the blame. Whether or not it's safe, it's still really common to store stuff in the oven, or maybe just leave some food in there to stay warm. And even if the adults follow the proper rules, you never know if the owners have had kids over recently who might have hidden a toy or wtv in there. I see it similarly to driving a car. Of course the car in front of you should drive safely and do proper stops/signals, but as the car coming from behind it is your responsibility to play it safe and keep proper distance in order to avoid accidents. Similarly, the person who owns the oven should use it properly, but as the person coming behind to use it (presumably when the owners aren't around), then it's your responsibility to check just-in case.

Not to mention leaving the house with the oven on, long enough to fill everwhere with smoke? Double mistake. Better to be safe than sorry.

There was smoke because something was in there that wasn't supposed to be, it could have been 5 minutes or less and still got smoky because it was cooking candle sticks instead of food. Also, just because a lot of people do it, doesn't make it right. Did you know, even if the oven is off, the pilot light is still on? That means there's still fire in there even if the oven isn't on. That is a huge risk, you have the potential to light stuff on fire anytime anything is in the oven. So if you store stuff in there, be aware, you're risking not only burning stuff should someone turn the oven on, you're also constantly risking your home and yourself should the pilot light catch it. There's a reason every fire department, fire safety cite/course, and oven instructions themselves say, DON'T store stuff in the oven even if it's off. I don't think the OP is to blame at all for using the oven as a freaking oven.

Since it takes a couple of minutes for a cold oven to get warm enough to burn stuff, not to mention (since the oven door is closed) it takes even longer for the smoke to fill an ENTIRE house, unless OP was being dramatic for the sake of humour I'm pretty sure she was out of the house for more than 5min. Likely she supervised her dog, let him run around a bit, and took the time to pick up after him (since it's not her home). And I'm not saying that since it's common to store stuff in the oven that it should be done. I'm saying since it's common, people should be aware that it is possible. Not to mention, as I said, what if a child or someone who didn't know better left something in the oven and the owners hadn't checked yet? Or what if the owners usually don't store stuff in the oven, but forgot to take their muffins or wtv out that one time? In this case the owners were being irrespeonsible, but since there are a million possibilities, I think OP should have checked the oven in someone else's home just in-case. Like I said, when safety depends on another person's actions, it's always better to be safe than sorry and check/control what you can in that situation.

Yes but this wasn't her house. Always look first. Cheap insurance against a $100,000 mistake.

Not to mention while fire departments do warn against storing stuff in the oven, they ALSO warn against leaving the house with the oven on. Even for 5 minutes. The owners chose to ignore advice against leaving stuff in the oven, and OP chose to ignore advice about leaving the house with an oven on. These are mistakes that anyone can make on an off-day... but to me, even if we ignore that OP didn't check first as a precaution, this situation still seems like they're both partially to blame.

It is not someone else's job to check if another capable person purposely left a hazard. It is the 1st person's job to not purposely leave a situation which could result in endangering another person. That's what the mother did, she purposely endangered not only the OP, but the house and everyone in it. One should not have to assume that the previous person left a dangerous situation, that person should just not leave it dangerous in the first place. As for the kid situation, that is irrelevant here as this is not that situation. However, you should not be leaving your kid unattended long enough around an oven for that to happen. And if they're old enough, you should have taught them that it's dangerous and they aren't to go near it. So if they leave stuff in there, that's on the parent, not the one who starts the oven.

In keeping with car themed analogies: If I were to own a car and it has faulty brakes, I would be at fault if someone were to use my car and got into an accident due to the brakes. You would also assume that if I am lending you my car, that it works and won't burst into flames. It isn't your job to bring my car to a mechanic and inspect damages, why would the OP have to check that they were placed in a dangerous situation when left with someone else's property? Negligence of the first party is not a defence when it has action upon a second party.

I guarantee that, when a woman complains a guy left the toilet seat up and then she fell in when she went to use it, the bulk of the comments will be from people saying she should have checked to make sure the seat was down before she tried to use it. Whether or not the oven is supposed to be a storage compartment or not is irrelevant. What matters is that (a) it's commonly used as one regardless; (b) it wasn't the OP's house so they (apparently) didn't know whether or not it was being used like that; (c) they didn't check before they turned on a potentially dangerous appliance that it was ready to be used; and (d) they then turned it on and left it completely unsupervised. The MIL might have been actually using the oven for its intended purpose, leaving the stuff in there to cool down after she had heated them up for a craft project or something. The person turning the oven on has the responsibility to ensure it is ready to be turned on (i.e. empty), the same as someone using a car has the responsibility to ensure it is ready to be driven forward (i.e. nothing in the way) before pulling out.

It takes a kid (even older ones misbehave) 5 seconds to put something in the oven....the time an adult might spend going to shower/toilet. It makes more sense to check the oven before using it, than to constantly check every single hazardous area in the house each time they use the washroom or wtv. And like I said, even people using the oven as recommended can simply forget they left something in the oven to cool down. That's why the child situation is relevant to the FML: it's not about the child, but the multiple possibilities that OP has no control over. In this case the MIL was irresponsible, but OP was not using her own oven, and therefore had no clue who had access to it recently and what they did. That's why she should have checked the oven before turning it on. And once again, leaving the house with the oven on? Big no-no. As for car analogy...you are legally supposed to replace faulty brakes/lights etc. Storing stuff in an oven isn't against the law, it's just not recommended. It's more like how when you enter a car (especially a borrowed one when the owner is not present) it's recommended you should walk around and do a full check, even if you aren't legally required to. Why? There are a million things which could be wrong: cat on wheels, something blocking a mirror/window, the driveway has something on it, etc. These are common issues, which may be someone else's fault, but since you are the next one getting into the car you are supposed to do the check. Recently my sister placed something reflective at the rear of the car and forgot it there. Later my brother drove the car without doing the recommended check, and got pulled over by the police. It didn't matter that my sister was the one who was irresponsible and forgot, my brother was the one who got the warning for not checking and creating a potentially dangerous situation (distracting other drivers). Other people should be responsible, but so should you: always check first, and don't leave the house with the oven on!

Actually, at least here in Germany, you ARE responsible if you drive someone else's car and it's faulty. You need to make sure any vehicle you drive is safe to use. There's no reason not to have a quick look in the oven before turning it on. As many already said, there might be so much stuff in there. Leftovers, previous make that were kept in there to stay warm, something that got forgotten... or something that want supposed to be in there in the first place but for whatever reason ended up in there.

I didn't put anything in the oven. lol. I preheated it.

You are 100% correct. But this is the exact reason you *always* look in the oven before turning it on. The consequences could be a house burned down, and the 2 seconds to look are trivial in comparison. Just look first and you'll never be sorry.

They were on a decorative cookie sheet with a glaze type coating on it.