I also have the same problem. Pls advise solution. Thanks.

I found the a solution that works for me, go into your themes and delete everything. Glass should then work. There is most likely a more direct method but I don't feel like tinkering so brute force works for me.

do what helix says. it works :)

You should not have to remove the other themes. Just make sure that the default theme is enabled.

I had the same issue and all I had to do was enable the default theme and restart, not remove any other themes.

I know it's only a beta, but I would have thought that they would enable the default theme by... default!

I have a similar problem but my theme says it is incompatible.

Fixed, problem was a windows 7 theme

I have a similar problem. When I first installed FF4b1, it reported that the Default theme was incompatible with FF4. Strangely, that has resolved itself without any help from me, and I am supposedly using the new FF4b1 default theme. However, my FF window still has the ordinary windows title bar, including min/max/close buttons, and the Firefox button is on the same row as the tabs.

See attached screenshot, or http://andstuff.org/ff-ui.jpg

Suggestions?

I just want to make sure you are using this on Vista or Windows 7 as XP or before does not have Aero.

John, ah, ok, yes, I am using XP. Didn't realize that Aero was only half-working on XP. Thanks.

By me, the default theme was marked incompatible several times (in the new add-on manager), and I had to use a little step-around, but simple solution. I just:

1. Closed Firefox 4 preview
2. opened an older version of Firefox
3. enabled the default theme
4. closed the older version
5. opened Firefox 4 preview

However, I admit bug (577098) is a weird bug