Excellent! Thanks for the information. No prizes for guessing what I'll be doing sometime today - no prizes either for guessing who's very likely to be reinstalling Firefox later (I work on the premise that if it can go wrong then it probably will).
The concerns raised in your post were given due consideration at the time of download and as usual, an A.V. scan was applied to the downloaded file. After installation another A.V.scan was carried out along with scans by Ad-aware, A² and Spybot - they all came out clear. The 'Read Me' file reveals an answer, of sorts, it also reveals that the programme works along the same lines as dagwood's link which would, in all probability, provide more potential for optimisation than the programme.
This is an extract from the read me text, re. the profile location - Version 1.6.3 (June 9th, 2004) - Once again the location of the user profiles has been changed in the new nightly builds. Since this location probably will stay the same for Firefox 0.9, Mozilla Optimizer now handles this new situation! It is a translation from the original German text so, consequently, not as clear as it could be. I may be wrong (nothing new there for me), but I don't see it as too sinister. Fingers crossed.