1. A computer-implemented method for installing a browser extension in a browser application, the method comprising: receiving, in a main process of the browser application running on a computing system, a browser extension installation package for installation in the browser application, the browser extension installation package including a plurality of constituent files of the browser extension; extracting a public key from the browser extension installation package; and validating a digital signature of the browser extension installation package using the public key, wherein: if validation of the digital signature is unsuccessful, installation of the browser extension is canceled; and if validation of the digital signature is successful, the method comprises: launching a sandboxed sub-process of the browser application; in the sandboxed sub-process, transcoding or recoding at least one of the plurality of constituent files, the at least one transcoded or recoded file replacing a corresponding original constituent file of the plurality of constituent files in the browser extension installation package; after the transcoding or recoding, passing the constituent files from the sandboxed sub-process to the main browser process; and in the main process of the browser application, installing the browser extension to the browser application using the at least one transcoded or recoded constituent file.