Como trocar o UserAgent do Firefox sem plugins

Eu usava um complemento que fazia essa tarefa automaticamente, mas depois de varias atualizações do navegador ele deixou de funcionar e eu não sei se ele ainda é compatível com a versão atual da raposa.

Bem eu estava precisando fazer um teste emulando um navegador móvel e não tinha tempo para ficar correndo atrás de plugins então tive que descobrir como se faz manualmente, veja como se faz:

1.Abra o Firefox e digite about:config na barra de endereço.
2.Clique com o botão direito e em “Nova preferência” selecione “String…”
3. Na caixa de dialogo que surgirá digite “general.useragent.override” e em seguida a string que você quer usar ex:

Mozilla/5.0 (Linux; U; Android 2.3.7; pt-br; X10mini Build/GRI40) AppleWebkit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1

Para testar seu novo UserAgent visite essa página: https://rotinadigital.net/useragente.php

Mais para que isso serve mesmo? Veja o resultado quando visitamos a página do Google:

Lista de UserAgentes:

Navegadores – Windows
Internet Explorer 8 (Windows XP) Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727)
Internet Explorer 7 (Windows Vista) Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0)
Internet Explorer 6 (Win XP) Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
Internet Explorer 5.5 (Win 2000) Mozilla/4.0 (compatible; MSIE 5.5; Windows NT 5.0 )
Internet Explorer 5.5 (Win ME) Mozilla/4.0 (compatible; MSIE 5.5; Windows 98; Win 9x 4.90)
Firefox 3.5 (Win XP) Mozilla/5.0 (Windows; U; Windows NT 5.1; pt-br; rv:1.9.1.1) Gecko/20090715 Firefox/3.5.1
Firefox 3.0 (Win XP) Mozilla/5.0 (Windows; U; Windows NT 5.1; pt-br; rv:1.9.0.1) Gecko/2008070208 Firefox/3.0.1
Firefox 2.0 (Win XP) Mozilla/5.0 (Windows; U; Windows NT 5.1; pt-br; rv:1.8.1.14) Gecko/20080404 Firefox/2.0.0.14
Google Chrome 2 (Win Vista) Mozilla/5.0 (Windows; U; Windows NT 6.0; pt-br) AppleWebKit/530.5 (KHTML, like Gecko) Chrome/2.0.172.37 Safari/530.5
Google Chrome 0.2.149.29 (Win XP) Mozilla/5.0 (Windows; U; Windows NT 5.1; pt-br) AppleWebKit/525.13 (KHTML, like Gecko) Chrome/0.2.149.29 Safari/525.13
Netscape 4.8 (Windows Vista) Mozilla/4.8 [en] (Windows NT 6.0; U)
Netscape 4.8 (Win XP) Mozilla/4.8 [en] (Windows NT 5.1; U)
Opera 9.25 (Windows Vista) Opera/9.25 (Windows NT 6.0; U; en)
Opera 8.0 (Win 2000) Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; en) Opera 8.0
Opera 7.51 (Win XP) Opera/7.51 (Windows NT 5.1; U) [en]
Opera 7.5 (Win XP) Opera/7.50 (Windows XP; U)
Avant Browser Avant Browser/1.2.789rel1 (http://www.avantbrowser.com)
Netscape 7.1 (Win 98) Mozilla/5.0 (Windows; U; Win98; pt-br; rv:1.4) Gecko Netscape/7.1 (ax)
Multizilla (Win xp) Mozilla/5.0 (Windows; U; Windows XP) Gecko MultiZilla/1.6.1.0a
Opera 7.5 (Win ME) Opera/7.50 (Windows ME; U) [en]
Netscape 3.01 gold (Win 95) Mozilla/3.01Gold (Win95; I)
Netscape 2.02 (Win 95) Mozilla/2.02E (Win95; U)

Navegadores – Mac
Safari 125.8 (Mac OSX) Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/125.2 (KHTML, like Gecko) Safari/125.8
Safari 85 (Mac OSX) Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/125.2 (KHTML, like Gecko) Safari/85.8
MSIE 5.15 (Mac OS 9) Mozilla/4.0 (compatible; MSIE 5.15; Mac_PowerPC)
Firefox 0.9 (Mac OSX ) Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; pt-br; rv:1.7a) Gecko/20040614 Firefox/0.9.0+
Omniweb563 (Mac OSX) Mozilla/5.0 (Macintosh; U; PPC Mac OS X; pt-br) AppleWebKit/125.4 (KHTML, like Gecko, Safari) OmniWeb/v563.15

Navegadores – Linux/Unix/BeOS
Mozilla 1.6 (Debian) Mozilla/5.0 (X11; U; Linux; i686; pt-br; rv:1.6) Gecko Debian/1.6-7
Epiphany (Linux) Mozilla/5.0 (X11; U; Linux; i686; pt-br; rv:1.6) Gecko Epiphany/1.2.5
Epiphany (Ubuntu) Mozilla/5.0 (X11; U; Linux i586; pt-br; rv:1.7.3) Gecko/20040924 Epiphany/1.4.4 (Ubuntu)
Galeon 1.3.14 (Linux) Mozilla/5.0 (X11; U; Linux; i686; pt-br; rv:1.6) Gecko Galeon/1.3.14
Konqueror 3 rc4 (Linux) Konqueror/3.0-rc4; (Konqueror/3.0-rc4; i686 Linux;;datecode)
Konqueror (Gentoo) Mozilla/5.0 (compatible; Konqueror/3.3; Linux 2.6.8-gentoo-r3; X11;
Firefox 0.8 (Linux) Mozilla/5.0 (X11; U; Linux i686; pt-br; rv:1.6) Gecko/20040614 Firefox/0.8
ELinks 0.9.3 (Kanotix) ELinks/0.9.3 (textmode; Linux 2.6.9-kanotix-8 i686; 127×41)
Elinks (Linux) ELinks (0.4pre5; Linux 2.6.10-ac7 i686; 80×33)
Links 2.1 (Linux) Links (2.1pre15; Linux 2.4.26 i686; 158×61)
Links 0.9.1 (Linux) Links/0.9.1 (Linux 2.4.24; i386;)
Opera 7.23 (Linux) MSIE (MSIE 6.0; X11; Linux; i686) Opera 7.23
Lynx 2.8.5rel.1 (Linux) Lynx/2.8.5rel.1 libwww-FM/2.14 SSL-MM/1.4.1 GNUTLS/0.8.12
w3m 0.5.1 (Linux) w3m/0.5.1
Links 2 (FreeBSD) Links (2.1pre15; FreeBSD 5.3-RELEASE i386; 196×84)
Mozilla 1.7 (FreeBSD) Mozilla/5.0 (X11; U; FreeBSD; i386; pt-br; rv:1.7) Gecko
Netscape 4.77 (Irix) Mozilla/4.77 [en] (X11; I; IRIX;64 6.5 IP30)
Netscape 4.8 (SunOS) Mozilla/4.8 [en] (X11; U; SunOS; 5.7 sun4u)
Net Positive (BeOS) Mozilla/3.0 (compatible; NetPositive/2.1.1; BeOS)

Navegadores de PDA / Smartphones
iPhone OS3 (Safari 4 Mobile) Mozilla/5.0 (iPhone; U; CPU iPhone OS 3_0 like Mac OS X; pt-br) AppleWebKit/528.18 (KHTML, like Gecko) Version/4.0 Mobile/7A341 Safari/528.16
iPhone Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en)
TOOLBARS
MegaUpload Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; Alexa Toolbar)

SPIDERS de buscadores
Googlebot 2.1 (New version) Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)
Googlebot 2.1 (Older Version) Googlebot/2.1 (+http://www.googlebot.com/bot.html)
Msnbot 1.0 (current version) msnbot/1.0 (+http://search.msn.com/msnbot.htm)
Msnbot 0.11 (beta version) msnbot/0.11 (+http://search.msn.com/msnbot.htm)
Yahoo Slurp Mozilla/5.0 (compatible; Yahoo! Slurp; http://help.yahoo.com/help/us/ysearch/slurp)
Ask Jeeves/Teoma Mozilla/2.0 (compatible; Ask Jeeves/Teoma)
scoutjet Mozilla/5.0 (compatible; ScoutJet; +http://www.scoutjet.com/)
Outros SPIDERS 
gulperbot Gulper Web Bot 0.2.4 (www.ecsl.cs.sunysb.edu/~maxim/cgi-bin/Link/GulperBot)
Email Wolf EmailWolf 1.00
grub client grub-client-1.5.3; (grub-client-1.5.3; Crawl your own stuff with http://grub.org)
download demon Download Demon/3.5.0.11
omni web OmniWeb/2.7-beta-3 OWF/1.0
winHTTP SearchExpress
ms url control Microsoft URL Control – 6.00.8862