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Spoofing Firefox 53 (and newer versions) on Windows 2000 and XP

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Just to prove another point about artifical web requirements, I was on LinkedIn today and I noticed that the site will redirect you to https://www.linkedin.com/error_pages/unsupported-browser.html if you are using an "unsupported" browser.

However, at the bottom of the page it also gives you the choice to continue on: https://www.linkedin.com/?allowUnsupportedBrowser=true

Continuing on does not provide a stripped down version of the site, it loads just as it would in a "supported browser".

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On 7/5/2017 at 11:07 PM, Tripredacus said:

[The] user agent you are using causes the site to send different code for you to use, code that would be usable on the actual browser you were pretending to be.

Up until a few days ago, I was running Firefox 34.0.5 with per-site spoofing (youtube.com and google.com) as FF43 to get rid of YouTube's nagging of using an outdated browser.  Now, using Firefox 46.0.1, I'm still using the same spoofing ("spoofing down"?) but it's to get back the "older" YouTube layout.  With FF34, I was used to browsing YT with zoom set 3x larger because I find the thumbnails and videos too small using the default zoom level.  With FF46, the YT video size is somewhat locked to "full width" (I can't size it), and using the x3 zoom level, the comments section that normally displays below a video drops all the way to the bottom to make way for a squished-in Related Videos section.  In order to get the Comments and Related Videos sections displayed side by side again, I need to unzoom a little but that turns the thumbnails too small again.  By spoofing as FF43, YT will provide FF the older layout which is more flexible.

Note: I haven't tested which FF version is the exact turning point for YT to switch to the new layout.  It could be 44 or 45.

I have these add-ons installed to spoof the UA on a per-site basis:

User-Agent JS Fixer 1.3.1-signed.1-signed


If you go to Add-ons > Extensions and click Options next to the UAControl entry, you can enter your own custom sites and user agents.  I use the following for both www.google.com and www.youtube.com:

Mozilla/5.0 (Windows NT 5.1; rv:43.0) Gecko/20100101 Firefox/43.0

YouTube also seems to be using a different global font using newer versions of Firefox which I find harder to read.  Spoofing as FF43 doesn't change it back, so I use "user CSS" to work around this.  If you want to know how to do it: In FF's profile folder, create a new folder called "chrome".  In there, create a new text file named userContent.css (no .txt at the end) and put this code inside:

@-moz-document domain(youtube.com){
    *{font-family:Arial !important}

You need to restart Firefox after each change as it won't use new additions on the fly like Opera 12 and earlier did.

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  • 9 months later...

Is it possible with I.E.8 without using UAPick?





Adding custom User-Agent strings

You can add custom user-agent strings to this tool by editing your registry.

Create a new REG_SZ named CustomUAList inside HKEY_CURRENT_USER or HKEY_CURRENT_USER \Software\Bayden Systems\UAPick.  The list uses a pipe-delimited list of UA names and values. 


I.E.11 on XP= Mozilla/5.0 (compatible; Windows NT 5.1; Trident/7.0; rv:11.0) like Gecko

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  • 2 months later...

Although I don't generally spoof Firefox, I do spoof Chromium 54 as the latest version of Chromium.

Right now, I'm pretending to be running Chromium 69.0.3497.86.

Together with ProxHTTPSProxy it works for many websites, however I still rely on Firefox for some of them that misbehave or have bugs.



"C:\Programmi\Advanced Chrome\chrome.exe" --user-agent="Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.86 Safari/537.36"

Edited by FranceBB
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@Sampei.Nihira about Basilisk. I f you had not set in about:config the general useragent.compatmode.firefox and general.useragent.compatmode.gecko to true, Basilisk would have passed the test with flying colours.

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All of those internet trackers are going to love this:


As one would expect, some websites will go into IE6 compatibility mode (the ones that still have it implemented) such as Google and Bing. Unfortunately, some websites are afraid of IE6 and will refuse to connect on that basis alone.

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  • 4 weeks later...

I have a question......I am currently trying out RT's Palemoon offshoot browser and I really am impressed.   The speed difference from FF 52.9.9 ESR is extremely noticeable and the resources consumed are much much lower.   The Plug in container alone consumed a lot of CPU cycles when functioning of Firefox 52.9.0 ESR.   The HTML5 and mp4 support on plaemoon (newmoon) is great as well......

My Question has to do with the user agent.   I have went to a couple of web sites which display a notice that my browser is outdated and that I should upgrade although I am running Version 28.1.0a1 on Windows XP sp3.   Is there a way to spoof this browser to prevent receiving these "out of date" notifications?


Edited by Dclem
added more info
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There are a number of preferences that affect the user agent in the about:config page.

  1. general.useragent.compatMode.firefox is a Boolean preference, which tells PM/NM and Basilisk/Serpent to spoof Firefox. It defaults to "false" in PM/NM and "true" in Basilisk/Serpent. You could set that to "false," and these browsers would then identify themselves more accurately, but few Web sites recognize PM specifically, so this may just confuse them even more.
  2. general.useragent.compatMode.version is a string preference that defaults to 52.9 and tells PM/NM (and Basilisk/Serpent) which Firefox version to spoof. So the simplest answer to your question is to change this to the FF version you want NM to spoof, say, 60.2.
  3. general.useragent.override is a string preference you can create to send whatever string you assign as the user agent. Using this you can pretend to be an iPhone using Safari or any other platform/browser combo you want. You'd need to know the user agent string for the combo you wanted to be, of course.
  4. general.useragent.site_specific_overrides is a Boolean preference that defaults to "true." You could set this to false to temporarily turn this feature off to test/debug specific Web sites, but the default of "true" allows NM to recognize additional preferences of the form....
  5. general.useragent.override.facebook.com = "<custom user agent string to be sent to facebook.com>"

The idea behind those last two is that you don't have to send every Web site the same user agent; helpful if spoofing FF 60.2 (or whatever) causes some websites to send content NM doesn't handle properly.

Edited by Mathwiz
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Mathwiz said:

general.useragent.compatMode.version is a string preference that defaults to 52.9 and tells PM/NM (and Basilisk/Serpent) which Firefox version to spoof.

Ah yet another pref, wasn't aware of that one yet :)

But it gets yet more complicated:
Acc. to goanna.js in omni.ja, the file with almost 2000 default prefs, there's also a Gecko-compat:

For Goanna-browsers version PM26+28:
6. general.useragent.compatMode.gecko = true/false

While Goanna-browsers version PM27 are completely different!
7. general.useragent.compatMode = 0/1/2 (INT)

In K-Meleon7677-Goanna27 it produces:
0 = Goanna + K-Meleon
1 = Gecko + Goanna + KM
2 = Gecko + Goanna + Firefox + KM

Results with K-Meleon74-Goanna26 (v20180718) on my system:
FF-false / gecko-false:
Mozilla/5.0 (Windows NT 5.0; rv:2.2) Goanna/20140105 K-Meleon/2.2.0
FF-false / gecko-true:
Mozilla/5.0 (Windows NT 5.0; rv:2.2) Gecko/20100101 Goanna/20140105 K-Meleon/2.2.0
FF-true / gecko-true:
Mozilla/5.0 (Windows NT 5.0; rv:38.9) Gecko/20100101 Goanna/2.2 Firefox/38.9 K-Meleon/2.2.0
FF-true / gecko-false:
Mozilla/5.0 (Windows NT 5.0; rv:38.9) Goanna/2.2 Firefox/38.9 K-Meleon/2.2.0

(am slightly confused now about the 2.2.0 at the end, thought had gotten KM74 in older tests, on XP, does the system influence this?)
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Thanks! I saw those preferences but wasn't sure what they did, so I didn't mention them.

It may be better to just ignore the whole mess and put your preferred user-agent string in general.useragent.override. That way you can spoof the Windows version as well as the FF version of your choice. Some sites are starting to balk at NT versions less than 6.1 (Win 7).

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