Cross-browser layout testing for an online store

We are releasing an updated version of our online store and want to make sure the layout renders correctly and consistently across all popular browsers and devices. We need an attentive QA specialist who will systematically walk through the key pages: home page, category listings, product page, shopping cart, checkout flow and the customer account area. The layout must be verified in Chrome, Firefox, Safari and Edge, as well as in mobile browsers on Android and iOS. Different screen resolutions matter a great deal, from small smartphones all the way up to wide desktop monitors. We expect detailed bug reports that include clear reproduction steps, screenshots, and the exact browser name, version number and device where the problem appears. We are particularly interested in the behaviour of the responsive grid, the accuracy of margins and padding, font readability, and how dropdown menus, modal windows and forms behave in each environment. After our development team fixes the reported issues, a round of regression testing will be required to confirm that the changes did not break adjacent blocks or other pages. A structured report with defect priorities and improvement suggestions is very welcome. Experience with e-commerce projects and a solid understanding of common layout compatibility issues will be a big plus. In your proposal, please describe which devices and browser combinations you have available and how you organise your testing process.