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My Firefox was just updated to Quantum and looks like user-agent is incorrect. It's now:

Mozilla/5.0 (Windows; U; Windows NT 5.0; rv:1.8.0.3) Gecko/20060426 Firefox/1.5.0.3

All websites, also mozilla.org, show me "Your browser version is old, please update." But after I first run this version, I was informed that this is latest, new Firefox.

Due to this I cannot do anything and also can't install User-Agent switcher which is worked with previous Firefox version.

How I can restore Firefox?

J.Mae
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  • [User-Agent switcher](https://addons.mozilla.org/en-US/firefox/addon/user-agent-switcher-revived/) works just fine with Firefox 57. Moreover, your user-agent string looks wrong: maybe leftover from some extension? My FF user-agent in 57 looks correct: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0 – Dexter Nov 17 '17 at 08:07
  • Did you try https://support.mozilla.org/en-US/kb/how-reset-default-user-agent-firefox ? Do you have any add-ons enabled? – Nickolay Jan 09 '18 at 13:16

2 Answers2

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Try going to about:config and check if privacy.resistFingerprinting is set to true.

That setting will spoof the user agent; changing it back to the default of false solved this issue for me.

cam8001
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  • Excellent suggestion.In my case was setting the version to 52. And last but not least was also preventing to save/restore the window size between sessions. – mins Apr 28 '18 at 14:50
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I'm having the same issue. I have multiple computers and each computer is stuck on a different user/agent when the update occurred. Obviously if you used an add-on, whatever the setting was at update is the one you have been branded with. If you do a full delete and reinstall it should fix it. A real pain, but another option may be to dowload a newer user/agent add-on and try to change it that way.

ekhumoro
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Exc
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