Hello
Sorry, actually speak German.
For me has helped Exit
1 Firefox closed
2 Open the file in Firefox profile pref.js
where the line user_pref (" browser.uiCustomization.state "
Search in the line nav- bar
after \ " wrc -toolbar -button \ "
this inserted , \ " window- controls \ "
doing it then look like this
"nav-bar\":[ ....., \ " wrc -toolbar -button \ " , \ " window- controls \ ",.....
stored and firefox started