Most Glass Jars are microwave safe and you should have no problem microwaving the glass jars.
However there are some types of glass that cannot be safely microwaved at least for too long before they break.
The glass jars made today are safe to microwave though however some of the older glass jars may not be microwave safe so use caution when microwaving them.
I have microwaved glass jars and glass bowls a lot and never had one break yet though.
The worse thing that can happen though if the glass jar you're microwaving isn't microwave safe is that it breaks inside the microwave and you have to clean up broken glass and whatever is in the microwave.
The new glass jars and bowls made today will usually say they are microwave safe but sometimes they don't say they are even though they can be microwaved.