You are mentionning two Privacy issues here: Circumvention of censorship & password protection.
When it comes to government firewalls, it is wise to use widely spread softwares, as they have been tested a lot and are known to work as safely as you can find. The reference here is Tor and is used daily by insurgents in countries famous for their restricted internet access like Syria or China.
For your password privacy, this is not a topic I am very knowledgeable in, but I would advise you to not use any extension on your browser when typing a password. I would not even trust the browser itself. If whatever you are doing is highly sensitive, I would suggest using Tails that comes bundled with… Tor!
For your specific application (Browsec), there are several signs that you shouldn't trust it:
- it is closed source (debatable, but you don't know what happens behind)
- has very little review online (drawbacks of not being famous)
- says they collect your data and may transmit it to a government
- state that the traffic goes through their network, hence any access to an unencrypted website, they can read it all. possibly SSL protected ones aswell depending on implementation.