While developing a rails app, I was in the google chrome inspect element console testing an ajax link when all of the sudden I noticed 12 errors of the same kind:

I have no clue what is happening here, but my app works just fine regardless. However, When I pull my app up in firefox, my app does not even load. I get stopped and this error pops up:

I dont even know what else to say here because I am completely stumped.
Ok, I found what was the problem was. When trying to get the bootstrap dropdown buttons to work the other day, I have rearranged the application.js folder to load bootstrap before jquery. I changed this:
to this:
At the time, this fixed the bootstrap dropdown problem. However, I now I realize that when bootstrap calls jquery, it will not have been loaded yet. Thus, the error
$ function does not exist. Just changed the lines back to the proper order and all is now well.