FAQ

General FAQ. For the technical FAQ, see the manual.

Is it really natively headless?

You see windows during the execution of your script? It's normal. Until Firefox 56, Gecko, the rendering engine of Firefox, couldn't render web content without a graphical window.
With Firefox 56+, you can launch a headless SlimerJS by adding a --headless flag on the command line. For older Firefox, and only on Linux, you can launch SlimerJS with xvfb. See the documentation about the headless mode.

What is Gecko?

Gecko is the core engine of Firefox.

Which version of Firefox is SlimerJS compatible with?

It runs with Firefox 52 and higher versions.
Officially, SlimerJS is only compatible with stable versions of Firefox until Firefox 59.

Why SlimerJS is not compatible with Firefox 60 and higher?

The Ghostbusters team of Mozilla decided to kill XUL extensions into Firefox some years ago, and so many of internal API of Firefox became unstable. Then it became more and more difficult to update SlimerJS at each new version of Firefox, as those internal API changed, disappeared etc. This ghost trap worked so well that at some points, it even became impossible to adapt SlimerJS without rewriting it entirely. Because of lack of time and motivation, the main developer stopped the development of SlimerJS in 2018 and decided in 2021 to officially end the project.

Why is it called "SlimerJs"?

Slimer is the name of a ghost in the movie "GhostBusters". As you may know, the Firefox source code uses some references from this movie, and since PhantomJS, CasperJs and other related tools, is a matter of... ghosts ;-)

I don't find anymore the "Standalone" edition like for SlimerJS 0.9. Where is it?

There are no more "standalone" edition, since Mozilla has ceased to build and maintain XulRunner. There is only the "lightweight" edition.

Can CasperJS be launched with SlimerJS?

Yes, since SlimerJS 0.8, and with CasperJS 1.1beta1 or higher. Just launch CasperJS as usual by adding --engine=slimerjs on the command line.

How can I contribute?

You can contribute in many ways:

• Report bugs or ideas of improvements into "issues" on github
• Improve the code by providing patches. SlimerJS is entirely in Javascript!! See instructions to contribute.
• Improve the Documentation. It is stored in the github repository.
• Improve the web site. The web site is also stored in the github repository.
• Other ideas? Discuss with us on the mailing list (see the community page).

Is there a build of SlimerJS containing the latest improvements?

Yes, each time a bug fix or an improvement is made in the repository of SlimerJS, a build is made. This is we call "nightly build". Since these are development versions don't use them in production.
Download the archive from the stable branch (which contains only latest bug fixes) or from the master branch (which contains latest improvements for the future major release). You can view the documentation from the master branch online here.

Why are there no tests on the WebServer object in the source code?

This module is based on the httpd component of Mozilla used for their own unit tests, and that is already heavily tested