addon doesn't work on 52.9.0 ESR

[theultramage]

Version information for Window Titler on AMO states "Works with firefox 42.0 and later" (or 48.0+ for earlier versions). However, when I try to install it on Firefox 52.9.0 ESR, I get "The add-on downloaded from this site could not be installed because it appears to be corrupt". Browser console reports:

addons.webextension.<unknown>	ERROR	Loading extension 'null': Reading manifest:
Error processing commands._execute_browser_action.suggested_key.default:
Value must either: match the pattern /^\s*(Alt|Ctrl|Command|MacCtrl)\s*\+\s*(Shift\s*\+\s*)? ([A-Z0-9]|Comma|Period|Home|End|PageUp|PageDown|Space|Insert|Delete|Up|Down|Left|Right)\s*$/,
or match the pattern /^(MediaNextTrack|MediaPlayPause|MediaPrevTrack|MediaStop)$/

The offending bit in manifest.json is

  "commands": {
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Alt+Ctrl+T"

Furthermore, the addon itself doesn't work. Trying to use the button to change window title gives:

TypeError: this._recipeManager is null

Saving of the addon's settings doesn't work either:

TypeError: key is undefined

If this addon is intended for and tested on the recent Firefox (Quantum) framework, I suggest defining it as such (I think on AMO it's version 57+).