Web App Comprehensive Testing -- 2

I'm seeking a thorough testing of my web app across various parameters. The testing should cover:

- Functionality: Ensuring every feature of the web app works as intended
- User Interface: Checking the app's usability and overall user experience
- Performance: Assessing the app's speed, responsiveness, and stability under load

The web app needs to be tested on:

- Desktop: Testing how the app performs on a standard computer
- Mobile: Ensuring the app is optimized and functional on smartphones

Please note, the testing doesn't need to cover tablets or Safari browser as of now.

Ideal skills for the job include:
- Proficiency in both desktop and mobile testing
- Strong understanding of web app functionality and user interface
- Experience with performance testing

Any experience you have in automated testing tools will be a plus. Thank you!