For desktops/laptops
running Windows/Mac/Linux
Firefox
and its variants, including
Pale Moon (versions newer than
24.7.2 have compatibility issues with some add-ons; and even for PM 24.x, currently the main GM add-on page will mysteriously only offer to install an older-than-necessary 0.9.22 version, but you can get the equally-compatible
1.15 from the archived versions instead),
Cyberfox (64-bit),
Waterfox (64-bit),
Firefox Ultimate
**
Greasemonkey for Firefox** ('GM') -
Mozilla Add-Ons page -
website
This is the origin of the userscripts concept, available for Firefox since 2005, still up-to-date as of 2015.
A competing extension called Scriptish is also available, but it hasn't been updated since June 2013 and has issues, so just stick with the better-known and better-supported Greasemonkey for Firefox.
Chrome
and its variants, including
Chromium,
SRWare Iron, and
Comodo Dragon (and Chromebooks)
**
Tampermonkey for Chrome** ('TM') -
Chrome Web Store page -
website
From Feb 2010 / v4 through
May 2014 / v35 (though it already became somewhat more difficult after
July 2012 / v21), Chrome was able to run some userscripts as natively-installed pseudo-extensions without Tampermonkey being installed. But that method doesn't support some script features; and since May 2014, Chrome on Windows will disable any such pseudo-extensions (and manually-installed regular extensions) every time you restart the browser, because they didn't come from the official Chrome Web Store. Just install Tampermonkey instead, which also provides more advanced script-management options and feature support, and then install your userscripts into Tampermonkey. (Chrome on Mac and Linux aren't affected by that policy change, but you're still better off using Tampermonkey anyway.)
A competing extension called NinjaKit (primarily intended for Safari) is also available, but it hasn't been updated since June 2013 and has issues, so just stick with the better-known and better-supported Tampermonkey for Chrome.
Opera
From 2012 / v15 through present, 'Opera Next'
controversially became a Chrome variant. For this generation of Opera, use:
Tampermonkey for Opera Next -
Opera Add-Ons page -
website
'Opera Classic' (aka 'Opera Presto') included built-in basic support for userscripts from April 2005 / v8 through 2012 / v12 (and small
updates to v12 in 2013 and 2014), through an
inconvenient interface and with limited feature support. For this generation of Opera, it's better to instead use:
ViolentMonkey for Opera (both Classic and Next) -
Opera Add-Ons page -
website -
direct download of Opera Classic versions
Be sure to "check the *Allow interaction with secure pages* in Privacy settings of the extension panel as this option is not ON by default and it prevents VM from working on HTTPS pages."
ViolentMonkey supports more features than the v12 built-in script support. But on v15+, which doesn't have its own built-in scripts support, Tampermonkey supports more features than ViolentMonkey.
Opera Classic (v12) does
not support IndexedDB, a storage method used by a few of the more complex scripts, including HitDB. Expect other feature limitations too.
Safari
Tampermonkey for Safari -
website
Quietly released in
Nov 2014; not available in Apple's official Safari extensions site, but can be downloaded from the official Tampermonkey site. Supports Safari v5 and higher, on both Mac and Windows (Safari hasn't released versions for Windows since
v5.1.7 in May 2012).
As of
Feb 2015, has a minor bug where if the first website you visit after restarting Safari has one or more userscripts set up to run on it, the scripts won't load properly until you refresh the page or visit another website.
Safari versions before v7.1 do
not support IndexedDB, a storage method used by a few of the more complex scripts, including HitDB.
Previous options for running userscripts in Safari, which were buggy and had limited feature support, included:
Creammonkey (2006-2007) and
GreaseKit (2007-2008) (only for Safari on Mac, up to v4; require
SIMBL framework), and
NinjaKit (
2010-2012) (for Safari v5 on Mac and Windows).
Internet Explorer
GreasemonkIE - for IE7+? -
website -
Crossrider install page
Released in
Aug 2014. Built using the Crossrider extension framework, which
says it supports IE7 and up (IE8, IE9, IE10, IE11...). The author
says "I’ve accounted for some differences between Firefox and IE, but I’m sure I’ve missed a few.", so expect unknown feature limitations.
TrixIE WPF4.5 - for IE10?, IE11 -
website
Previous options for running userscripts in Internet Explorer, which were buggy and had limited feature support/compatibility (partly their fault, partly IE's fault - particularly the older IE versions, which used more proprietary variants of Javascript commands), included:
Turnabout Advanced (2005 - IE6);
Trixie (2005 - IE6, but
reportedly works in its limited capacity in at least IE7-IE9 too, with increased problems in IE10-IE11);
Greasemonkey for IE (2006 - IE5?, IE6); and
IE7Pro's
IEScripts (2007-2010 - IE6, IE7, IE8).
One of IE's particularly odd feature limitations (which I don't know if any of the above userscript-running tools build in fixes for) is that it refuses to run any Javascript containing console.log statements, which are used by many userscript authors, unless you have the Developer Tools console open at the time. Press F12 to open Dev Tools, and then you can minimize its area, or manually adjust the height as short as possible, or detach it into a separate window that can then be minimized.
SeaMonkey
Based on Firefox/Netscape, but has limited extension availability.
Scriptish for SeaMonkey -
Mozilla Add-Ons page -
archived website
Scriptish hasn't been updated since June 2013, the developer is non-responsive, and its website is dead as of this writing (Feb 2015). But it reportedly still works in recent SeaMonkey versions, and the only other option is unofficial:
Greasemonkey for SeaMonkey -
website
There was previously an official Greasemonkey version that supported SeaMonkey, but that
appears to no longer be the case. This unofficial modification of the official Greasemonkey for Firefox is available instead, and up-to-date as of this writing (Feb 2015). (There is also another unofficial modified version
here which is VERY outdated, not recommended. An
automated add-on converter tool is also available, which may or may not be helpful.)
Maxthon
Based on Internet Explorer, but has branched out a lot.
ViolentMonkey for Maxthon -
Maxthon Extension Center page -
website
Note: "Some of the GM_* functions may not work due to the API limitations of Maxthon.",
particularly GM_setClipboard.
QupZilla
QupZilla has included a built-in version of GreaseMonkey since
July 2012 (occasionally
updated).
Note: "some GM_ functions does not work, mainly script resources and persistent settings."
Midori
Midori has included built-in basic support for userscripts since at least 2011.
Note: Apparently does
NOT support scripts that @require external libraries such as Jquery, or any GM_ functions.