Been in China now for 11+ years.
This app is the most reliable I've found here. Works like a charm for work and private. I use it on my PC/Android and its flawless. No idea why there are only 20ish reviews for this app. I am sure every single foreigner in China would love this app.

Its not free, but I haven't buying this. Just renewed for another year.

Best VPN provider for China (need to subscribe, not free, but quite cheap), by far the number one if you live or work in China (I have tried many other services during 10+ years). The VPN add-on is working great. Sometimes servers are slow to respond despite the frequent updates, but the VPN access has never been broken (it was often broken or slowed down with most other providers). However, the add-on v.2.0.8 have not been updated for a while, would like to see some new improvements.

This addon doesn't work.
Check permissions before installing and make sure you trust it before installing.
I don't recommend using this addon even to premium users.
I would like to also mention that Nothing here is free.
\\Firefox76.0.1

Требует регистрацию!

Best VPN in China! Most stable service when most VPNs fail. The extension allows fine tuning of which website should be accessed with the VPN or with a direct connection, without having to disconnect and reconnect all the time.

不适合中国

12VPN is one of the best services to use in China and this extension works without any issues. Even though I prefer to use auto-proxy, sometimes it's useful to have a fallback option.

Best VPN service in China