Uwe Brauer wrote:

I noted since a couple of days a slow down when I try to submit a contribution. Is there anything I could do like enhance the cache of my browser?

There can be several cause, most of them are not related to client side caching :)

When you submit a contribution, the software need to write in the master database (which is handling all writes for all projects). Then the software need to reparse the whole page and send it back to you (and flush various caches).