Since CSS3’s gradient backgrounds are fairly new the functionality in all browsers is different.
Here is a sample of how you can achieve cross-browser functionality:

background-color: #2B2B2B;
background-image: mix(rgba(255, 255, 255, 0.5), rgba(255, 255, 255, 0), 50%);
filter: "progid:DXImageTransform.Microsoft.gradient(startColorStr="rgba(255, 255, 255, 0.5)", EndColorStr="rgba(255, 255, 255, 0)")";
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