Methods and apparatus for installing browser extensions using sandboxed processes are disclosed. An example method includes receiving a browser extension installation package in a main browser process, placing the browser extension installation package in a temporary directory and launching a sandboxed sub-process of the browser application, where the sandboxed sub-process has access to the temporary directory. The example method includes, in the sandboxed sub-process: unpacking a compressed, archived file of the installation package into the plurality of constituent files of the browser extension and transcoding or recoding at least one of the plurality of constituent files, where the transcoded and recoded files replace their corresponding original constituent files. The example method includes, after the transcoding and/or recoding, passing the constituent files back to a main browser process and installing the browser extension to the browser application using the transcoded and recoded constituent files.