I am currently trying to learn how to develop Firefox add-ons, but for my misfortune, I faced a problem before I even start doing so. I downloaded the demo add-on provided by the Firefox developer team which is called "Borderify" and can be seen here: GitHub. After that, I opened WinRar, and converted the folder to a .XPI file. However, when I try to install it manually on my Firefox browser I got this message "This add-on cannot be installed because it appears to be corrupted". I will be grateful if someone points what I've done wrong.
Note that just packing the files and renaming the .ZIP file to an .XPI to install it doesn't work. If you want to test and debug the extension, you need to install the extension temporarily. To do so, go to about:debugging and click Load Temporary Add-on, then choose the XPI file to install the add-on. You can also load the add-on from the sources without packing it to an XPI by simply choosing its manifest.json file.
To get the XPI file to install as expected, it needs to be signed. This will be done automatically when you publish it on addons.mozilla.org (AMO).
来源：https://stackoverflow.com/questions/44507730/installation-error-this-add-on-cannot-be-installed-because-it-appears-to-be-co