FlowCrypt is another browser extension. I'm not sure about any advantages or disadvantages it may have compared with Mailvelope. I read somewhere it supports signing messages but I haven't tried whether mailvelope also can do that.

FlowCrypt is another browser extension.

While Mailvelope can work with system GnuPG installation optionally, I think FLowCrypt cannot. Mailvelope also requires a license if you want to use with a corporate account (or you must rebuild it yourself).

I'm not sure about any other advantages or disadvantages it may have. Authors claim Flowcrypt's code is cleaner. But because of the system GnuPG integration, I decided to use Mailvelope at the end.