The general way to find out how well your computer performs is to use benchmarking software. There are plenty of benchmarking tools to test the performance of various pieces of your computer hardware. There are actually specific browser-based benchmarks too, websites designed to test your browser’s performance in a variety of tests.
Before you run any benchmarks, it’s highly recommended that you shut down as many other applications as possible to give your benchmark as much access to the system resources as possible. It’s also recommended that you ensure that you have the latest version of your browser installed and have up to date graphics drivers. Browser extensions can also interfere with performance results so you should ideally temporarily disable them. The key is to try to make your tests as fair as possible, so your results are comparable.
The Basemark Web 3.0 benchmark, available here offers a suite of 20 different tests that include things like resizing support, page load times, HTML5 support, and CSS support.