Firewall error after champion select FIX! At least it worked for me!
About a year ago, a nice fellow by the name of rftiiv15 submitted a possible solution to the infamous firewall error that appears for some LoL players. I do not take credit for this fix, I'm simply making a discussion about it to spread the word.
I myself was plagued with this problem for the last few months, and tried nearly everything to fix it, and this guy fixed it for me in two steps. Kudos to him, and be sure to thank him for all his hard work! I just found this Reddit post a few minutes ago, and it fixed my problem when it re-surfaced again! :)
NOTE: You may need to apply this fix after patches because the files you rename in the fix might get renamed by Riot programmers or the default patch settings.