One of the add-ons that I came to rely on in the past is the Greasemonkey extension. Unfortunately it was one of the add-ons not working in Firefox 4.

I first tried to force compatibility on the add-on, with mixed results as it was not working correctly afterwards (take a look at this guide on how to force compatibility in the Firefox web browser)

If you look at the official Greasemonkey site at Mozilla you notice that the add-on is only compatible with versions up to Firefox 3.6, and the same information is offered on the web page of the developer. The last release dates back to April 2010.

What many users do not know is that the developer publishes nightly builds of Greasemonkey on the same server. Nightly builds are development versions of the add-on which often contain additional features or improvements.

In the case of Greasemonkey, they add Firefox 4 compatibility. Just install the latest nightly build from the listing to make Greasemonkey compatible with Firefox 4. Please note though that nightly builds may contain bugs. Firefox will automatically recognize Greasemonkey nightly updates and offer to install them automatically, so that it does not need to be done manually.

All installed userscripts worked fine after installation of the latest Greasemonkey nightly. Let us know your experience in the comments.

While the Firefox web browser does not have that feature build in there is a Greasemonkey script with a similar functionality. Page Scroll is a script for the Greasemonkey extension for the Firefox web browser that will display transparent lines on all websites. It will display the lines on top by default and display the other lines if the user is working with the Page UP / Page Down keys, the mouse wheel or by dragging the scroll bar around.

This is however the only known script that is mimicking Opera’s Scroll Marker feature. Some users might not like the fact that the script is active on all websites by default. A right-click on the Greasemonkey icon and a selection of Manage User Scripts makes it possible to customize the sites list. Change the wildcard symbol to urls to activate the script only on those selected urls. Make sure to use wildcards yourself if the domain is making use of subdomains and directories.

Please note that the script seems to have difficulties on some websites to display the transparent scroll lines correctly. It should work on most sites perfectly however. Google Chrome users might get the script working in their web browser as well if they check the Google Chrome Greasemonkey article.