Steps to reproduce
Edge is not injecting stylesheets properly on first load for browser extensions. With “run_at” set at "document_start". On first attempt to load an extension it can fail doing so and a page refresh is required. But if the extension remains installed after page loads and browser restarts this does not happen. Only on browser first load. The same extension running on Chrome/Firefox does not have this issue.
An example can be seen here: https://i.imgur.com/TeTE5r4.png
Stylesheets aren’t loaded correctly and causes page breakage, after a refresh it works as intended.
It is also possible to cause this by clearing all browser cookies/cache (all options) in the clear browsing data and restart the browser.
Setting “run_at” to “document_end” in the manifest gives a better visualization of the problem. Page loads, extension loads then stylesheets are left behind.
An extension test case is attached and is best tested on google. Load the extension in and browse to google. Then refresh the page. On first browse the background will stay normal, after a refresh it will go red. On other browsers the change does not require a page refresh.