Hello,
So excuse for my english but I am very bad 
Google Translate will be my friend !!!
After a certain time of surfing I have my tabs that become black under firefox.
And when I restart a new session (by having extinguished the previous one) firefox becomes normal again.
What’s the solution please ?
Sounds like you’re running low on memory. How much RAM do you have & what OS are you using?
By the way, it’s not the appropriate place to ask this question lol 
why it’s not the apropriate place ???
6 Go RAM
Windows 10
This forum is for add-on questions. For general Firefox support, please visit https://support.mozilla.org/