Add-on “appears to be corrupt” when trying to install my add-on's .xpi file in Firefox

Question

I am trying to install an extension in Firefox 45 (same happens with Firefox 49), but Firefox does not allow me to do that, indicating that

Answer 1

I think there is something not clearly documented, I'd like to share my experience.

1. Developed my extension and zipped all the files
2. Selected On your own for How to Distribute this Version step and uploaded .zip to AMO
3. Then, on the next page, I see a signed .xpi file available for download. I downloaded it and tried to install via "about:addons -> Install Add-on from file"
   1. I get corrupt add-on error in this case
4. After receiving e-mail from amo-editors@mozilla.org, I went to my add-on's page and clicked on .xpi file link there and it worked!