hello, please try resetting all customized preferences in about:config that start with network.dns. or network.http. to their default values & make sure that you've set up firefox to directly connect to the internet and don't use a proxy (in firefox > options > advanced > network > connection - settings...).

How do I reset them. I don't know what they are supposed to be.

you can right-click & reset each individual entry

Please also see and continue in /questions/936722

_{Thanks for reporting the duplicate madperson. I will lock this one.}