Fixes #202 - width discrepency for firefox

[kevnk]

I simply switched the order of the if statement to use jquery first if available because it's more reliable (and works for FF) than the raw javascript (which didn't work for firefox)

[pfiller]

Thanks @kevinkirchner. The way you fixed this meant that Prototype was still getting the broken version. It also made the window.computedStyle call totally unnecessary in the jQuery version.

After you shared this, I did some digging and I think offsetWidth may be a safe and reliable option. I've opened #1172 which seems to solve the FF issue and gives us a cleaner method. Mind taking a look to make sure it solves the problem you were seeing?

[kevnk]

Commit be1a255 does indeed solve out Firefox issue. Thanks!