Slightly, but the difference is noticeable enough to mention. Mainly due to bloat that Firefox has picked up over years of updates and the fact that Brave is built using Chromium, Google open-source browser tech that is super fast to start with.
No, Firefox and Brave are both very secure and have robust privacy features. Brave just enacts these features by default whereas Firefox allows you to set your level of privacy. In the end, Brave just cuts out the middle man.