In my case there were changes in configuration.
Today I removed Sandboxie Plus and Mozilla Firefox completely.
I added Opera as main browser.
The reason for the change ?
Already with Chrome in Sandbox browsing the Internet became slower. Then with Firefox it seemed fine already.
But after some time it also turned out that everything goes slower.
The time has come for Opera, to which I tried some time ago. I used the portable version for a long time.
Today I installed it normally and really everything works faster.
I do not want to go into what was the reason - I guess it was Sandboxie.
If anything, I have a copy of the previous setup (FF + Sandboxie) Macrium Reflect.