VPN issues are to be directed to their VPN support to resolve. This is a End user forum for FF problems. FF doesn't configure or help with VPN settings issues.

WestEnd, can you please stop telling people we cannot help with insert thing because you may not understand or look for possible answers. There may be people here who has done VPN's like OpenVPN with Firefox on Linux that can help.

MahdiG2 said

It doesn't happens by other browsers or in Windows by local dns I mean government dns sink

I assume you got the OpenVPN setup already since you think it works in other web browsers on the Ubuntu system.

Did you make any changes in Firefox or only just setup the VPN on Ubuntu in general.

https://support.mozilla.org/en-US/kb/connection-settings-firefox

Though you may get help in a Ubuntu forum. One poster said he could not get the OpenVPN to work in Firefox but worked after a reboot. https://askubuntu.com/questions/1022662/firefox-not-using-vpn

Never used VPN on Linux but wanted show that people can still help here unlike what WestEnd claimed above.

Try:

• https://medium.freecodecamp.org/how-to-setup-a-vpn-for-free-or-paid-on-linux-62e1a93d04f3
• https://www.google.com/search?sa=N&num=100&q=OpenVPN%20firefox%20linux%20dns

In dns leak test, it shows that firefox sends requests both to local and VPN dns server. Which means Firefox doesn't encrypt its requests through vpn, just changes its dns address to vpn dns (un-encrypted), which causes ISP sends local dns result as vpn dns result.

Use Tor

I cannot trust Tor nodes. probably most of the nodes run by china or Russia. (I'm not telling that west activists shouldn't care about anonymity I can some example legitimate activisms, that should care about it, beside whistle blowers)

I installed snap store version of it, and not this problem in it. Also there was no problem in firefox 58 (ubuntu 16)

MahdiG2 said

I cannot trust Tor nodes. probably most of the nodes run by china or Russia. (I'm not telling that west activist shouldn't care about anonymity I can example legitimate activisms, that should care about it, besides whistle blowers)

LOL, more like FBI,, Malwarbytes does a good job of catching bad nodes. But a lot was fixed with that about a year ago.

Ok, so the Snap version has fixed you up then, great !