Firefox incompatable

I'm not sure why it is happening to me more often now than when I started using Firefox a year ago but I seem to be hitting sites that are not compatible with Firefox. Lately the two biggest culprits have been Shaw.ca bill payment site, U of A’s WebCT, and Edmonton Catholic School District's report card webpage. Sure I can see my students’ report card but I can't edit them. I can understand ECSD not being up to par. It's not like they have a huge budget to throw at such things but seriously Bell Canada. I might start asking for a paper bill if they can't shape up. I eventually paid my bill using Internet Explorer. For those not familiar with Explorer it is an alternative to web browsing. I wouldn't recommend it. ;)