Doesn't this methodology fall over the next (and subsequent) time your addins are updated? I average eight addins in Firefox, and most of them are updated at least once a month, so I'd think my "fingerprint" would change every other week.
For most advertising purposes, you don't need to track a user for that long anyway. Conversion tracking, view-through attribution, frequency capping, retargeting, interest-based behavioral targeting... sure, businesses would ideally prefer that the unique identifier last for thirty days, but 'every other week' would capture the bulk of the benefit.
A truly shady business could rely primarily on cookies, local storage, etc. but use browser fingerprinting only to repopulate user IDs after data deletion. Incorporating extensions into the fingerprinting could make this technique a lot more effective.