From https://developer.mozilla.org/ :
The Web Integrated Development Environment (WebIDE) is a browser-based IDE that enables software development or Web development. It can be accessed from a web browser, such as Google Chrome or Mozilla Firefox, allowing for a portable work environment. For Mozilla it was an essential component for the development of Firefox OS, but now it has come in handy for KaiOS.
WebIDE allows you to connect the Firefox Developer Tools to a number of other browsers. With it, you first set up one or more "runtimes (an environment in which you'll run and debug the app and that could be a KaiOS device or a Firefox OS simulator installed on the desktop itself)".
Next, you create an app or open an existing one. If you want to create a new app you can start with a template that includes the directory structure and the minimum boilerplate you need to get started, or a more complete template that shows how to use a privileged API.
WebIDE shows your app's files in a tree, and you can edit and save them using a built-in source editor. Of course, you don't have to use the built-in editor: you can develop your app entirely outside WebIDE, and only use it for debugging. Finally, you can install the app in one of the runtimes and run it. You can then open the usual suite of developer tools (the Inspector, Console, JavaScript Debugger and so on) to examine and modify the running app.
To use any WebIDE function, your device must be debug-enabled (take a look at the DEVICES section), in which case you can access and configure it as follows:
Enable the debug mode on your device.
Connect the device to the PC using a USB cable.
Open WebIDE and connect to the "Remote runtime" (this should work on the official Kaiostr emulator), if not seen, start the adb forward tcp:6000 localfilesystem:/data/local/debugger-socket command and click again on "Remote runtime". If an error message about build date mismatch appears, you can safely ignore it. If the connection doesn't work, try rebooting the phone, running the adb forward command and connecting again. NOTE: the adb forward command is not needed using the offical emulator "KaiOSRT".
Select the application's folder in the "Open packaged app" button of WebIDE.
With the triangular "Play button" at the top center of WebIDE, the app will be installed on your phone.
More details on the jailbreak in the dedicated guide: Official Jailbreak
KaiosRT (KaiOS RunTime) is the official KaiOS emulator. This useful tool works for any Linux distribution (not just Ubuntu). Using KaiOSRT it is possible to interact with your device by simply connecting it in Debug mode, without having to use the adb forward command.
https://developer.kaiostech.com/docs/02.getting-started/01.env-setup/simulator
It is possible to download the emulator using the wget program:
wget https://s3.amazonaws.com/kaicloudsimulatordl/developer-portal/simulator/Kaiosrt_ubuntu.tar.bz2Extract the archive using tar:
tar -axvf Kaiosrt_ubuntu.tar.bz2Enter the extracted folder and untar the internal archive again:
cd kaiosrt-v2.5-ubuntu-20190925163557-n378
tar -axvf kaiosrt-v2.5.en-US.linux-x86_64.tar.bz2
Enter the kaiosrt folder and finally run the kaiosrt executable file to open the program:
cd kaiosrt
./kaiosrt
Or just download and run KaiosRT using these commands:
wget https://s3.amazonaws.com/kaicloudsimulatordl/developer-portal/simulator/Kaiosrt_ubuntu.tar.bz2 &&
tar -axvf Kaiosrt_ubuntu.tar.bz2 &&
cd kaiosrt-v2.5-ubuntu-20190925163557-n378 &&
tar -axvf kaiosrt-v2.5.en-US.linux-x86_64.tar.bz2 &&
cd kaiosrt &&
./kaiosrt
This method was tested also on Windows 10, by using WSL (Windows Subsystem for Linux). See this video on Youtube
Pale Moon is a fork of Firefox with substantial divergence. The main differences are the user interface, add-on support, and running in single-process mode. It retains the highly customizable user interface of the Firefox version 4–28 era and included WebIDE until the v28.6.1 (2019-07-25). Available for Microsoft Windows and Linux (with other operating systems in development) on archive.palemoon.org.
NOTE: you should disable automatic updates
Firefox 59 was the last version available for the Boot To Gecko development, and the last one with a workable WebIDE for KaiOS devices (older versions also work well, especially Firefox 49 or Firefox 52.9 ESR). All the Firefox releases are available for all the platforms on the official website archive.mozilla.org.
NOTE: you should disable automatic updates
If you also want to take screenshots from your device screen from command line, see screen mirroring