I believe both are acceptable, I have seen "dans le frigo" more often though. In an earlier lesson there was a bit of a discussion on "dans son bureau" vs "à son bureau".. both technically mean the same thing, its as subtle as "in his office" vs "at his office". I am guessing it works the same way with the fridge? Although "at the fridge" does sound a little strange to an anglophile's ear...
duolingo (Rémy) has relented. I received this e-mail today:
You suggested “There is a bottle in the refrigerator.” as a translation for “Il y a une bouteille au réfrigérateur.” We now accept this translation. :)
Yahoo! I wonder if any other refrigerator-is-not-fridge instances have been changed.
I'm glad you were able to bring this to his attention. There are so many opportunities for improvement in the English language side of the French course and it requires a high level of expertise on both sides of the equation. To his credit, he developed this course pretty much all by himself. But it has to overcome some of the limitations that were built into it which include raising the bar on the quality of the English translations.
à /a/ - au /o/ - aux /o/ - ou /u/
So, "au" and "aux" sound the same before a consonant. You can also listen to the pronunciation here: http://translate.google.com/#fr/en/%C3%A0.%20au.%20aux.%20ou