Bugzilla Bug 42519
EP20 | Customize: Should remember its previous window size.
Method:
1. Select the Favorites tab
2. Launch Customize
3. Click the restore button in top right
4. Resize the window so it looks right in 1024x768 resolutions
5. Restart application
Result: Application launched in maximum window size.
Logged In: YES
user_id=1110932
Originator: NO
As far as I know, this is not possible with icewm.