Shell Context Menu Commands for Kindle Files Only Showing for Certain Extensions

Question

A while ago, I added a number of context menu commands to import Kindle books into Calibre and convert them to EPUB (under HKEY_CLASSES_ROOT\Amazon.Kindle.content). All associated extensions are set in the registry to point at Amazon.Kindle.content. This has been working great up until today, when the commands stopped showing up for .mobi files. When I right click a .azl, .azs, .azw, .azw3, .azw4, .prc or .tpz file, they appear and work as expected. But not for .mobi. Here are my registry entries for .azw and .mobi — they look exactly the same to me so I have no idea what is going on:

[HKEY_CLASSES_ROOT\.azw]
@="Amazon.Kindle.content"

[HKEY_CLASSES_ROOT\.mobi]
@="Amazon.Kindle.content"

jscholes@rebus:~$ cat >azw.reg
Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\.azw]
@="Amazon.Kindle.content"

jscholes@rebus:~$ cat >mobi.reg
Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\.mobi]
@="Amazon.Kindle.content"

jscholes@rebus:~$ diff azw.reg mobi.reg
3c3
< [HKEY_CLASSES_ROOT\.azw]
---
> [HKEY_CLASSES_ROOT\.mobi]

Answer 1

The solution, which I probably should've tried sooner, was to set the default program for .mobi files to Kindle for PC. Nothing has been altered in HKEY_CLASSES_ROOT.mobi after doing this, but the commands now show when right-clicking a .mobi file.