Old browsers do not support modern web standards (HTML5, CSS Grid, modern JavaScript). There is no fix for this other than using a "User Agent Switcher" extension to pretend you are a different browser, though that rarely fixes rendering issues.
This is the safest source. It contains every version of Firefox ever released.
Current Firefox blocks addons that are not signed by Mozilla. Old versions (pre-2015) did not enforce this. older version of firefox
: Authentic older versions are available via the official Mozilla FTP archive .
If you need to access old government or corporate systems that require Java Applets, modern Firefox will not work. Old browsers do not support modern web standards
: Modern Firefox uses "downgrade protection." To force an older version to open an existing profile, users may need to run Firefox with the --allow-downgrade command-line parameter. Alternatives to Downgrading
Downgrading is not as simple as running a new installer; you must manage your data to prevent corruption. It contains every version of Firefox ever released
Providing a "complete guide" on older versions of Firefox is a broad topic, covering everything from why you might need one, how to find it, and the critical safety precautions you must take.
If the menu option doesn't stick: