У вашего броузера проблема в совместимости с HTML5
A common error that can ruin a day or two of your league life :p Simple fix and things should be back to normal.
-File names-
League of Legends/Config/
Delete the file 'game.cfg' and 'input.txt'
or
League of Legends/RADS/projects/lol_game_client and lol_game_client_en_us
Delete both of them and run the Repair tool afterwards.
Twitter: @dotdotryan