--- a/js/src/vm/ForkJoin.cpp
+++ b/js/src/vm/ForkJoin.cpp
@@ -404,16 +404,17 @@ class ForkJoinShared : public TaskExecut
     // Requests that computation abort.
     void setAbortFlag(bool fatal);
 
     // Set the fatal flag for the next abort.
     void setPendingAbortFatal() { fatal_ = true; }
 
     JSRuntime *runtime() { return cx_->runtime(); }
     JS::Zone *zone() { return cx_->zone(); }
+    JSCompartment *compartment() { return cx_->compartment(); }
 
     JSContext *acquireContext() { PR_Lock(cxLock_); return cx_; }
     void releaseContext() { PR_Unlock(cxLock_); }
 };
 
 class AutoEnterWarmup
 {
     JSRuntime *runtime_;
@@ -1684,16 +1685,23 @@ ForkJoinSlice::ForkJoinSlice(PerThreadDa
     shared(shared),
     acquiredContext_(false)
 {
     /*
      * Unsafely set the zone. This is used to track malloc counters and to
      * trigger GCs and is otherwise not thread-safe to access.
      */
     zone_ = shared->zone();
+
+    /*
+     * Unsafely set the compartment. This is used to get read-only access to
+     * shared tables.
+     */
+    compartment_ = shared->compartment();
+
     allocator_ = allocator;
 }
 
 bool
 ForkJoinSlice::isMainThread() const
 {
     return perThreadData == &shared->runtime()->mainThread;
 }