This thesis investigates the performance of Fortinet's Next-Generation Firewalls (NGFWs), specifically the FortiGate 40F and 1500D models, under varying traffic conditions and security requirements. Given the increasing reliance on SSL inspection for network security and its potential impact on performance, this study aims to provide guidance for organizations selecting appropriate firewall solutions. To simulate real-world network conditions, this study utilizes a designed testbed to evaluate the performance of FortiGate firewalls in handling HTTPS traffic with and without SSL inspection and antivirus scanning enabled. This approach provides practical insights into the operational impact of these security features.Results reveal that while 1500D consistently outperforms the 40F firewall, both models maintain a consistent virus detection rate. However, CPU and memory utilization remain stable across both models even under heavy loads, suggesting bottlenecks within specialized security processors. This thesis demonstrates the crucial role of hardware accelerators, par-ticularly Content Processors (CPs), in determining NGFW performance. With its more ad-vanced CPs, the FortiGate 1500D demonstrates superior performance in handling high traffic volumes and complex security tasks compared to the 40F model, underscoring the importance of selecting firewall models based on specific network and security needs. These findings provide guidance for organizations seeking to balance protection against malicious traffic with optimal network efficiency.