My Firefox profile being corrupted, I had to dive a little bit into its salted directory. What I found there is just scary... Here are the contents of that profile:

GoogleToolbarData			extensions				places.sqlite
User_Gear.owg extensions.ini pluginreg.dat
adblockplus extensions.log prefs.bak
addons.sqlite extensions.rdf prefs.js
antbar extensions.sqlite rainbow-easel
blocklist.xml fireFTPprograms.dat scribefire.sqlite
bookmarkbackups fireFTPsites.dat search.json
bookmarks.bak firebug search.rdf
bookmarks.html foo.dat search.sqlite
bookmarks.html.sbsd.bak formhistory.sqlite searchplugins
bookmarks.postplaces.html foxyproxy.xml secmod.db
bookmarks.preplaces.html freerecord.sqlite sessionstore.bak
bookmarks.xml gm_scripts sessionstore.js
bookmarks_history.sqlite gtb-metrics.xml signons.sqlite
cert8.db hostperm.1 signons.txt
cert_override.txt imagescatch_autosave.owm signons2.txt
chatzilla jetpack signons3.txt
chrome jetpack-editor-code.txt tidy_base.html
chromeappsstore.sqlite jetpack-example-code.txt tidy_cleanup.html
compatibility.ini jetpack_ann.sqlite tplbug.sqlite
compreg.dat key3.db twitfactory.sqlite
content-prefs.sqlite kf.txt twitterfox_1.9.sqlite
cookies.sqlite kosa ubiquity_suggestion_memory.sqlite
cookies.sqlite.bak lightweighttheme-footer urlclassifier.sqlite
cookies.txt lightweighttheme-header urlclassifier2.sqlite
cookperm.txt localstore-safe.rdf urlclassifierkey3.txt
defaults.ini localstore.bak useragentswitcher
despin-scratchpad localstore.rdf venkman-settings.js
dh-conv-rules.rdf localstore.rdf~ weave
dh-media-lists.rdf messages.sqlite webappsstore.sqlite
dh-smart-names.rdf mimeTypes.rdf webchunks2.sqlite
downloads.sqlite minidumps xpti.dat
dta_history.xml permissions.sqlite
dustmeselectors-data persdict.dat

Hum, to say the least... Ok, some files there (*~ and *,bak) are mine, edited using emacs or another editor because I needed it. But I think user profiles should contain a addon-data/ folder with a subfolder per add-on, its name being the add-on ID of the add-on and that AMO editorial rules should force add-on authors to store *ALL* data there. It would then be easier to migrate, backup, delete, cleanup. Thoughts ? In particular is it ok to put sqlite databases in such a deeper folder for sqlite-based templates (I haven't checked yet)?