Oddly enough the course page is quite responsive with IE10 !
We have some really long course pages on when you turn editing on the loading time is 5x more than when the page is loaded without turning editing on , only in Firefox (27 ) though!
With both Chrome and IE , the average load time is around 7 sec but with FireFox its around 35 sec. I believe Firefox is taking a lot longer to load the JS files than IE and Chrome, could this be the case ?
Using moodle 2.6.3
Performace Overview seems OK
Zend Opcache enabled