This master thesis deals with the topic of browser extensions, their environment and analysis. The goal is to describe the extensions environment, online Webstores, that offers extensions and to show best practices for analysis and optimization of its extensions and their assets. Within the thesis you can find very precise analysis of online Webstores for Google Chrome extensions and Mozilla Firefox add-ons. Conclusions are made based on this analysis that include special characteristics of the previously mentioned browsers. The master thesis consists of two parts, theoretical and practical. The theoretical parts deals with the description of the browser extensions environment and it presents specific characteristics about online Webstores ...