network protocall error?

The other day i got this error in mt browser trying to access facebook. Then it happened on another site. This keeps happening randomly but if i hit the "try again" button then all is normal and i can access it. Malwarebytes find nothing. My firefox browser is set to delete cookies upon closing the browser but i have some site set to be allowed and retain cookies. But apparently i never did that for facebook so it can't be a corrupt cookie. I have had this error in the past but it;s always a case where i can hit try again and it never works. I find it odd i can hit that and then it all works again. What could cause random network protocall errors?

Thanks. I googled it a few times and i decided to clear cache which i was afraid to do at first for fear i'd lose some sort of saved data. But i did it and i think that worked. If it happens again tho i'll try that, thanks.