I apologize, I tested some more and found out, that it is actually related to the browser putting its data not into RAM but on my SD-Card (which serves as harddrive replacement) and is very slow, it seems that for an unrelated reason (I yet have to find out) it slowed down. Putting the temp data into RAM speeds it up to its original speed, though originally that was not necessary.
I apologize, I tested some more and found out, that it is actually related to the browser putting its data not into RAM but on my SD-Card (which serves as harddrive replacement) and is very slow, it seems that for an unrelated reason (I yet have to find out) it slowed down. Putting the temp data into RAM speeds it up to its original speed, though originally that was not necessary.