Because my Firefox says this add-on is corrupted, so I had to install older version. The older version works very well, so I hope newer version may be so.
Many users have this issue with WebExtensions, I'm not sure what's the problem, I think it has something to do with addon signing and I hear Mozilla is working on it.
You can set "xpinstall.signatures.required" in config to false as a quick workaround, or wait until it's resolved.
