addons.sqlite stores the information that appears in the Addons tab > Extensions - under the More button, along with AMO URL's for extensions that aren't setup to use that new feature.

extensions.sqlite stores data about installed extensions, replacing the extensions.rdf and extensions.cache files.

You don't really need the addons.sqlite file, but I don't know the ramifications of deleting the contents of that file and "locking" it to keep it from being used. Not that it stores a lot of data; only 320kb with 30 extensions installed.

Thanks for the reply and information.

The reason that I asked the question, is that FEBE does not work correctly and it appears to be due to the addons.sqlite file. Others on the FEBE forum are experiencing problems similar to mine with Firefox 4 and the FEBE development build for Firefox 4. I know it is the developer's problem to fix FEBE, but just to explain what is happening:

• Full Profile backup in FEBE backs up all extensions to a file named profileFx4{0 Beta Profile}.fbu in the folder designated for FEBE backups
• Selective backup is another matter:
  • Only some extensions (1-9 in my case, varies from day to day) get backed up individually in the designated backup folder
  • Exit Firefox 4 and rename addons.sqlite then restart Firefox 4 and all extensions get backed up in Selective backup

I am sure that FEBE's developer knows about these 2 files (addons.sqlite and extensions.sqlite) and their functions. In my case, after much experimentation, the problem appears to be related to addons.sqlite.

Thanks again.