I've seen this but I wasn't keen on using a browser extension. Also I sometimes access BF3 stats and Battlelog via the iPad when I'm on the upstairs PS3 and they only support Firefox and Chrome currently.
Have you tried it, Herm? If so, what do you think?
I've had it for a few days and to be honest it rubbish. It just adds extra % and hit/kill on weapons, also has a number of ribbons required next to the medal instead of having to do the math yourself. Has nothing for assignments, vehicles it just adds how many destroyed vehicles next to your amount of kills. On the bottom of the overview page it has Extended Player Statistics, which is just a graph version of the stats provided by battlelog anyway.
Other than that I've not noticed anything else, there is options you can alter/break but I've not looked at what they are/do.
They're just interpolating the available data from Battlelog. I like the results given by BF3stats.com which is the one that I used for BFBC2 and also the one used to create the signatures (which I've not done as yet as it needs recoding). BF3stats also shows you your 10 closest unlocks, 10 closest awards (stars, medals, etc) and your assignments on one easy screen. I just wish they'd make the site just a mite more reliable.