Many users on Mac have been reporting weird performance issues post Beta2 though we had done much work around performance improvement. Here’s a workaround to get rid of the unexplained CFB slowdown issues that you have been facing. Internal browser is created in Eclipse with SWT.MOZILLA type. We added this in beta2. There is a bug logged with Eclipse at https://bugs.eclipse.org/bugs/show_bug.cgi?id=287416. As per the bug report, SWT.MOZILLA type causes windowserver process of Mac to go crazy. So, what you can do now is disable Firefox preview option in CFB.
Go to Preferences->HTML->Editors->HTML->Preview. At the bottom you will see browser type listed. Uncheck Firefox, restart CFB. You might also need to uncheck Preferences->ColdFusion->Extensions->Use Mozilla browser for Extensions just in case you have it checked. Let me know if you still experience the gradual slowdown issue.