Firefox cache2 'doomed' folder
To completely turn off caching in Firefox, open a new tab and type about:config, then search for browser.cache.disk.enable and double-click it to set it to false.
Then delete the cache manually, restart Firefox, and your doomed files will be gone.
The current files are there because your cache is not 0 and that's why they are there, disappear and then get replaced by others... ;-)