Blackberry OS version 4.6.1.314 for Blackberry Curve 8520 device, which was released early November is now available for everyone. The update which is said to fix the browser issue can be installed from the Blackberry Desktop Manager. More detail here.

It took approximately 50 minutes to complete overall upgrade OS including back up and restore the data back.  If your OS currently run on 4.6.1.286, you may want to update although no major enhancement introduced.