I tried to do the problem and I couldn't, you probably have another extension that conflicts with the behavior. There are extensions that do the job of forcing a single URL to simulate a "standby" mode. If you can provide clear details of how the error occurs, including which addons you use, it will be easier to try to work around the problem so that you can enjoy this addon. Report in: https://github.com/brcontainer/prevent-duplicate-tabs/issues/new/choose