This is a standard feature in Safari, Chrome and Brave but on Firefox you need to manually set it for each page you visit the first time. There needs to be a setting for a default zoom/font for all web pages. Thanks.
Note ! Be careful when trying to modify layout.css.devPixelsPerPx If it's really but hugely exaggerated ... Like about:config is no longer accessible In this case, the solution is to stop Firefox start Firefox stop Firefox Then in the user profile https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data modify prefs.js level layout.css.devPixelsPerPx and reset to default value -1.0 and save prefs.js and start Firefox