Given Mozilla’s current release cadence (major version every 4 weeks), version 450 would be released approximately in the . That is 15 years from the time of this writing.
However, the internet is full of typos, misremembered numbers, and third-party repackagers. The most likely candidate for your search is (also styled as 4.5.0.1) — a real, albeit ancient, beta or experimental build from late 2011. mozilla firefox 450 1 old version
Do not enter your passwords, credit cards, or personal data into any browser version below Firefox 78 (released 2020). The "old version" you seek is a museum piece—admire it, emulate it, but do not daily drive it. the internet is full of typos