Use After Free and Out-of-bounds Write vulnerabilities totally appears in Firefox web browser. It looks that there are more vulnerabilities found! The code for all projects in the Mozilla family (such as Firefox, Thunderbird, etc.) … Contains images and CSS files to skin the browser for each OS (Linux, Mac and Windows) … Support code for calling JavaScript code from C++ code and C++ code from JavaScript code, using XPCOM interfaces. So the hit rate of above vulnerabilities indeed possible and it make Firefox unsafe. In short, please see below url for reference. It is a official announcement.

https://www.mozilla.org/en-US/security/advisories/mfsa2018-06/