Hi,

In the Firefox Options-> General -> Language there is: -"Choose your preferred language for displaying pages". Click on "Choose" and I believe by removing the language which you do not wish to have, in this case Vietnamese, the browser will display in the language you desire. Tell me if that solves your problem. Thank you.

Hello hdoanz,

Looking at your screenshot, it looks like this applies to menus only (?)

Did you download Firefox in English from here (?) :

https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

If so, please try to start Firefox with the -purgecaches command line switch - see the last comment in this bug report :

https://bugzilla.mozilla.org/show_bug.cgi?id=1564998

Try to add the full path to the Firefox installation folder.

• "C:\Program Files\Mozilla Firefox\firefox.exe" -purgecaches
• (64-bit Firefox) "C:\Program Files\Mozilla Firefox\"
• (32-bit Firefox) "C:\Program Files (x86)\Mozilla Firefox\"

Also see : https://developer.mozilla.org/en-US/Command_Line_Options

I live in the US and download Firefox from Firefox so I assume it's Firefox in English. I uninstalled Firefox from my computer, downloaded Firefox (78.0.1 version) from the link you sent and installed Firefox. Launch Firefox from the new installation, I got a suggestion to refresh Firefox that seems to remove old settings, cache data from my profile. After the refresh now Firefox shows everything in English. I verify the default language is English (United State) just like I had before. I believe somewhere in my profile (cache data) it retained Vietnamese and now it's gone after a refresh.

Many thanks for your help. H Doan

Many thanks for your help.

My pleasure   -   I'm really glad that you've got things back to normal !

Would you be so kind as to remove the Chosen Solution mark from my post and mark your own (last) post instead ?
After all :   you did way more than I suggested   -   well done !

(edit: typo)