Warning....this is quite a long article. But very interesting and worthwhile if you have Pyrex glassware in your home.
So, according to the article the formula for Pyrex has changed, not for the better. It was not changed due to new and better technology. Instead it was changed for economic reasons.
If you don't have time to read the article the most important take away is avoid thermal shock. That means that let a dish warm up a bit between the fridge and heat. No refrigerator direct to microwave or oven.