I recently wrote an article on Bucrowd forums about why prebuilt browsers are bad. I also explained the countermeasures of using security-based prebuilt browsers, such as OWASP Mantra, and HconSTF, and how it's easy compromise any penetration tester that is using the current version of these projects.
The article can be found here (Link).
In case the article or the forum went down for any reason, I have made a PDF copy of the article that can be downloaded from here (Link).
I have also provided a solution for penetration testers that uses OWASP Mantra and HconSTF in their daily work. The project I have done can be found here (Link).
In case you have any issues or questions, feel free to send me an email, I will respond to you when possible.