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I don't know a lot about your juniper, but they are sensitive and a number of things can cause browning: under or overwatering (if the roots are staying soggy), spider mites, fungal diseases, improper pruning... I would start by inspecting it carefully. If you shake some of the browned branches over a piece of white paper, you will be able to see if there are spider mites, which are very tiny. Dig down in to the soil near the roots to see what condition it is in.
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