Methods and apparatus for installing browser extensions are disclosed. An example method includes receiving a browser extension installation package in a main browser process, validating a digital signature of the installation package and launching a sandboxed sub-process of the browser application. The example method includes, in the sandboxed sub-process: respectively transcoding or recoding at least one of the plurality of constituent files, where the transcoded and/or recoded files replace their corresponding original constituent files. The example method includes, after the transcoding and/or recoding, passing the constituent files from the sandboxed sub-process to the main browser process and installing the browser extension to the browser application using the transcoded and/or recoded files.