When you press the "play" button at the top of the screen, you usually see your changes in the browser.
However, there are a number of changes which no amount of refreshing, closing opening browsers, saving the project etc will show, one of which is if you change the "first layout" in the project properties.
1) create a new project with 2 layouts.
2) put "layout 1" text box on first
3) put "layout 2" text on second.
Now hit preview which opens up your chosen browser.
You see layout 2.
Now in the project properties, change the first layout to be layout 1.
You still see layout 2.
Change the first layout as often as you want - you will only every see layout 2 in the browser.
Close and open your project.
Now you see layout 1.
Here is the capx I used to reproduce:
Just open it, preview (you should see layout 2).
Now change it to layout 1 - preview again and you still see layout 2.
Save, close and open the project - now you see layout 1.
I get the same problem with a number of other attributes and events.
using FF 14.1, windows 7 64 bit.