I would test it first...put a pyrex cup with about a cup of water int he microwave and the JaneRay in there empty....set the timer for 2 minutes full power, and the water should be boiling but the empty JaneRay bowl should not be hot....if it is, I wouldn't put it in the micro again.
Some of my antique stuff works fine....but other stuff doesn't.
Linda

I collect Jadite Fire-King. In the past, have popped a couple in the microwave, but they get pretty darned hot, so makes me think it might not last over time. I don't use mine in the microwave any more. I Googled your question and found the following 2 articles:

Is it safe to put Fire\-King in the dishwasher  or even a microwave? Microwave: Yes; Dishwasher: No. We have been using Fire\-King in our microwave for years without a problem. However, since Fire\-King glass was developed well before microwave ovens were available for domestic use, none of the earlier pieces are marked "Microwave Safe." Some Anchor\-Hocking patterns not marketed as Fire\-King are indeed made of the same "heat proof" borosilicate low expansion glass. One example is blue Bubble. We "nuke" our leftovers in blue Bubble flat soup bowls. Other non\-Fire\-King Anchor\-Hocking patterns, such as Charm, ARE NOT heat proof. Be sure to avoid using gold\-trimmed pieces in a microwave as well. I DO NOT recommend that you wash Fire\-King dishes in a dishwasher. They'll come clean all right, but over time, the original lustre will be replaced with a "dishwasher haze" \-\- an actual removal of a thin layer of glass that removes its value as well. In your shopping for old Fire\-King, you'll run across pieces that look like they've been sandblasted. Those were washed in a dishwasher. NEVER wash Peach Lustre or hand painted Gay Fad pieces in a dishwasher.

The Anchor Hocking Glassware Manufacturing Company

According to the Sparkle Plenty Glassware Company in Bar Harbor, Maine, the label Fire-King is an Anchor Hocking Company trademark for pieces made with low-expansion boroscilicate glass (Sparkle Plenty website).

The manufacturer advertised Fire-King glass as "heat proof," meaning that it could go in the oven, but not on top of the range. Although earlier pieces came out before the advent of microwave ovens, most Fire-King can go into the microwave, unless it has trim. Fire-King will lose its luster and coloring over time if placed in a dishwasher.

Not all Anchor Hocking pieces bear a mark. The glass pouring process obscures the distinctive signature when glass material accumulates inside the mold in repeated layers that build up over time. As a result, the company eventually used imprinted foil labels that came off during dish washing (Sparkle Plenty).

Read more at Suite101: Collecting Fire King Glass: Vintage Fireking Glassware Collecting Remains Popular http://collecting-ceramics-glass.suite101.com/article.cfm/collecting-fire-king-glass#ixzz0krMkH1Ei

If dish gets hot in the microwave, that means that it and not the food is absorbing the rays....if a dish gets hot in the micro, not only may your dish break but your food won't cook well.

Thanks!