Yeah some nights it doesn't do it at all like last night .......... Last night it never did it even once for me at all and the person was wearing the same outfit clothes, shape, skin, etc of when it did it.
It seems to be more of an issue on the weekend when there are more people on the SL Grid then anything even if there are only 3 people around me it will do it and then sometimes it won't like last night.
I believer the non-imposter avatars I have set to 30 I will try turning it down to 20 and see if that does anything for me.
Also I always have my world set to "Show Friends Only" no matter where I'm at so I only see friends in my view which is maybe never more then 4 most day and sometimes maybe 10 depending on the day but 90% of the time its usually never more then 4 avatars on my screen including mine.
When I had a computer tower with about the same RAM i had issues running the 64 Bit when i installed the 32 Bit i had no issues what so ever so there for that's why I'm running the 32 Bit viewer I don't even remember the issues I had cause I have not had a tower in over 3 years.
I know someone with the excat same laptop as me and I believe they can only run the 32 Bit as well not the 64 bit its been awhile since i even been around this person to even remember and they haven't had Firestorm installed in there laptop for a least 3 or 4 new versions of Firestorm to even ask them to check.
And as I said above it is not always an issue like last night it never did it even once for me I usually see it more on the weekend when the Grid is more busy sometimes during the week but it is very odd to happen during the week its more a weekend thing that i noticed.