crusti wrote: Both in Bianca and Cassandra Firefox will freeze randomly while navigating through YouTube
Could be that you still use an old version of the Flash plugin? I had that too. Upgrading to a newer version definitely helps. Can you check what the status of the flashplugin-nonfree
package is on your system? e.g. via Synaptic
Other than that I suggest not to open too many windows and browser instances at once when surfing around on YouTube ... the combination of too many open Firefox windows + YouTube seems to increase the likelihood of the freeze happening.
BTW, Did you try Opera ... I hate to recommend closed source software, but Opera seems to handle YouTube better than Firefox does.