Thanks for your review. I'm using local storage API which is quite unstable on browser restart scenarios (https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage). I need to change it for next release as I'm now getting warnings from Firefox add-in checks, it is not recommended to use this API for extensions anymore...
You can directly open an issue on Github for me to track this evolution (I've just enabled the feature on the repo for this purpose).
https://github.com/wakeuteu/socksproxy-firefox-addon/issues

Edit: Took me some times but v1.2.0 should finally bring this feature :-)