I just downloaded Mountain Lion and I'm using it with FW CS5.1, and i'm noticing all the same issues, as well as odd behavior with the selction tool not working and requiring triple or more clicks to select tools and shapes.
So dissapointing. I also use FW for a lot of my work-flow. In fact it's my go-to tool for anything that requires a quick graphic mock-up ( I always liked the way teh color-picker picked up colors from outside the workspace without switcing apps) and i rarely use it in the ways it's supposed to integrate with Dreamweaver. Still, I'm using it constantly, most days, and it's a real shame that it's so unstable in Mountain Lion