[Nook Touch Themes and Apps] nmyshkin:
Or not. I lifted and modified this section from another reader app, keeping only the formats supported by the Kindle reader:

<intent-filter>
<action android:name="android.intent.action.VIEW"/>
<action android:name="android.intent.action.PICK"/>
<category android:name="android.intent.category.DEFAULT"/>
<category android:name="android.intent.category.BROWSABLE"/>
<data android:host="" android:scheme="file"/>
<data android:host="*" android:scheme="file"/>
<data android:mimeType="application/x-mobipocket-ebook"/>
<data android:mimeType="application/azw3"/>
<data android:mimeType="application/mobi"/>
<data android:mimeType="application/prc"/>
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.VIEW"/>
<action android:name="android.intent.action.PICK"/>
<category android:name="android.intent.category.DEFAULT"/>
<category android:name="android.intent.category.BROWSABLE"/>
<data android:host="" android:scheme="file"/>
<data android:host="*" android:scheme="file"/>
<data android:pathPattern=".*\\.prc"/>
<data android:pathPattern=".*\\.mobi"/>
<data android:pathPattern=".*\\.azw"/>
<data android:pathPattern=".*\\.azw3"/>
</intent-filter>

I placed it within the <activity> brackets for com.amazon.kindle.reader.BookReaderActivity. That seemed sensible to me. Everything goes back together fine and I didn't break anything (or not much...) because I can still register the app.

But .mobi files (for example) just sulk when tapped in a file manager. There's a bit of a flicker, like it's thinking about maybe thinking about doing something, but that's it. A logcat extract shows:

I/ActivityManager( 1114): Starting activity: Intent { cmp=com.estrongs.android.pop/.view.OpenRecomm (has extras) }
I/ActivityManager( 1114): Starting activity: Intent { act=android.intent.action.VIEW cat=[android.intent.category.DEFAULT] dat=file:///sdcard/kindle/League%20of%20Spies%20-%20Aaron%20Allston.mobi typ=application/x-mobipocket-ebook flg=0x10000000 cmp=com.amazon.kindle/com.amazon.kcp.reader.BookReaderActivity }
E/TC ( 1564): KPICollector: 1649718249106 ActivityManager background {"component":"com.estrongs.android.pop/.view.OpenRecomm"}
E/TC ( 1564): KPICollector: 1649718249112 ActivityManager foreground {"component":"com.amazon.kindle/com.amazon.kcp.reader.BookReaderActivity"}
V/Activity( 1976): performResume()
D/EPD#ActivityResume( 1114): resetRegion 4
D/NATIVE-EPD( 1114): epd_reset_region: 0x10
D/EPD#ActivityResume( 1114): resetRegion 5
D/NATIVE-EPD( 1114): epd_reset_region: 0x20
D/EPD#ActivityResume( 1114): resetRegion 6
D/NATIVE-EPD( 1114): epd_reset_region: 0x40
D/EPD#ActivityResume( 1114): resetRegion 7
D/NATIVE-EPD( 1114): epd_reset_region: 0x80
D/EPD#ActivityResume( 1114): Disable EPD for 350ms!!!!!!!!
E/TC ( 1564): KPICollector: 1649718249253 ActivityManager background {"component":"com.amazon.kindle/com.amazon.kcp.reader.BookReaderActivity"}
E/TC ( 1564): KPICollector: 1649718249276 ActivityManager foreground {"component":"com.estrongs.android.pop/.view.FileExplorerActivity"}

It looks like maybe the reader activity is running in the background (with the file manager running in the foreground?

But that's that. It doesn't look like this is a way in. There's very little out there about this issue. I've found only two discussions so far, one unresolved and one part of a larger approach in the construction of an app. Not what I'm after.

Back to the drawing board.