Just found interesting tip to speed up Firefox.

mentioned here
http://www.samelis.ch/blog/mischa/in...er-performance
german:
these are the links there:
https://bytestopshere.wordpress.com/...gment-firefox/
http://www.mydigitallife.info/optimi...-applications/
http://www.crystalidea.com/speedyfox

I will start with speedyfox and observe.
be aware: overloaded bookmarks-list with duplicates and multiples will also trottle speed. there are addons to cure that.