There have been a number of posts in Theme and Extension threads that include a link to "fix" compatibility issues. Those "fixes" that are not posted by the developer will be removed for the following reasons:
1) If the theme is being actively developed by it author, it is likely to be updated in short order.
2) You do not have permission from the author to use his/her images.
1) If the extension is being actively developed it will be updated in short order.
2) If the extension is not being actively developed, you can rename it and post your updates to AMO.
The .xpi, which is always posted on a non- AMO/Author site, have not been vetted so it can include anything.