One benefit I would add is that cross platform support is great for browser extensions. Browsers already run on different OS's and devices. Browser API and extension API are fairly uniform among the major browsers. It's close to the cross platform support of general websites.
As an experiment I develop my latest browser extension on Firefox [1], Chrome, and Edge [2] at the same time to see how difficult it is to share the same code base. The difference is minuscule, like less than 0.01%. Chrome and Edge are essentially the same. Firefox is a bit behind in Manifest V3 support and needs a few lines Firefox specific API calls. The manifest files have a few differences. Overall, sharing the same code base is very feasible.
As an experiment I develop my latest browser extension on Firefox [1], Chrome, and Edge [2] at the same time to see how difficult it is to share the same code base. The difference is minuscule, like less than 0.01%. Chrome and Edge are essentially the same. Firefox is a bit behind in Manifest V3 support and needs a few lines Firefox specific API calls. The manifest files have a few differences. Overall, sharing the same code base is very feasible.
[1] https://addons.mozilla.org/en-US/firefox/addon/one-page-favo...
[2] https://microsoftedge.microsoft.com/addons/detail/one-page-f...
Edit: You might ask where the Chrome version. Well, I had a heck of time to create a new Google account for deployment. Stay tune.