Just some different fields in the manifest, and there are specifics that work completely different or are not available (for example favicons).
I have tried Chrome -> Firefox before and it was surprisingly easy. Safari is more difficult in my experience, it's missing complete API's like the bookmarks one.
Web extensions API is emerging and a lot of it is already somewhat standardized https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Web...
Just some different fields in the manifest, and there are specifics that work completely different or are not available (for example favicons).
I have tried Chrome -> Firefox before and it was surprisingly easy. Safari is more difficult in my experience, it's missing complete API's like the bookmarks one.