seamonkey 2.53.9 bug

seamonkey 2.53.9:
Whenever a non-default theme is loaded (including "modern"): session manager will die with a strange error. Is this a race condition being hit while applying styles and asynchronously loading the session manager extension?

Timestamp: 9/11/2021, 11:11:41 PM
Error: TypeError: browser[name] is undefined
Source File: resource://devtools/client/framework/gDevTools.jsm
Line: 158

Timestamp: 9/11/2021, 11:11:41 PM
Error: uncaught exception: 2147942487
Source File: jar:file:///C:/Users/wyatt/AppData/Roaming/Mozilla/SeaMonkey/Profiles/windev/extensions/%7B1280606b-2510-4fe0-97ef-9b5a22eafe30%7D.xpi!/packages/browserWindowOverlay.js
Line: 1349

Timestamp: 9/11/2021, 11:11:41 PM
Error: [Exception... "Illegal value'Illegal value' when calling method: [nsISessionStore::getClosedTabCount]"  nsresult: "0x80070057 (NS_ERROR_ILLEGAL_VALUE)"  location: "JS frame :: jar:file:///C:/Users/wyatt/AppData/Roaming/Mozilla/SeaMonkey/Profiles/windev/extensions/%7B1280606b-2510-4fe0-97ef-9b5a22eafe30%7D.xpi!/packages/browserWindowOverlay.js :: updateUndoButton :: line 1349"  data: no]

Timestamp: 9/11/2021, 11:11:41 PM
Error: TypeError: menu is null
Source File: resource://devtools/client/framework/browser-menus.js
Line: 223

Timestamp: 9/11/2021, 11:11:41 PM
Error: NS_ERROR_FILE_NOT_FOUND:
Source File: jar:file:///C:/Program%20Files/SeaMonkey/omni.ja!/components/devtools-startup.js
Line: 273