I think that I've found the problem that caused Write Area to reset the toolbar configuration in Firefox 4.
Let's hope that the rest of adjustments are fine and I can release this version soon (yes, it includes CKEditor, the 3.5 SVN. It weights 483 Kb, so I'm not sure about trying to remove more things that aren't too useful)
I've reduced 90Kb by removing the translations that had over 200 missing entries. It might make sense to even remove translations with over 100 missing entries.
Currently there's a problem as the toolbar Cut and Copy commands don't work like they used to do (without any warning), so I'll have to check what has been changed.
The current work is available in the "beta channel", you can get it in the Write Area page, and scroll down searching for "beta channel". I've removed several plugins, looked for unused files, and everything that I could find to easily reduce the size (changing the core to remove code for other browsers is not a valid option in the long term).
I've applied also some fixes that might not be available in 3.5, but I think that they provide a better experience. Some parts might not work correctly as the 3.5 still isn't finished and there might be unexpected bugs.