User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:55.0) Gecko/20100101 Firefox/55.0 Build ID: 20170418100213 Steps to reproduce: 1. Set extensions.webextensions.remote = true 2. Set xpinstall.signatures.required = false 3. Install https://github.com/gorhill/uMatrix/releases/download/1.0.0/uMatrix.webext.xpi 4. Install https://github.com/gorhill/uBlock/releases/download/1.12.1/uBlock0.webext.xpi Actual results: 1. ublock origin and umatrix both are doing their jobs, but have a blank browserAction popup (only the border is shown). 2. the umatrix icon is shown after a while on its button. 3. If you set extensions.webextensions.remote back to false, they are working as expected. Expected results: 1. the browserAction popup of ublock origin should be visible 2. umatrix' icon show be visible immediately I think bug 1353060 and/or bug 1356317 are related to this.