As of 2022 most of the old answers are quite outdated.
Installing unsigned extensions/addons/themes is not possible anymore for the Release versions of firefox, especially just copying them into the profile/extension folder ("sideloading", see here).
Only ESR, Developer, Nightly and Unbranded versions of firefox still allow installation of unsigned extensions.
Mozilla gives a nice Firefox workflow overview for creating extensions.
For running and debugging extensions you can use the tool web-ext or the following (both methods described in link above):
- in firefox open a new tab exteand type
about:debugging
- under
This Firefox
you can Load temporary Addon...
to load your extension
- (don't load a .xpi file, just select any file within the directory you develop your extension in)
- the extension is loaded and you can debug it
- you need to use the Browser Toolbox to debug extensions
- in case the devTools won't work make sure
devtools.chrome.enabled = true
in about:config
- when you made code changes you can click
Reload
in the debugging tab
Finally, after coding and testing, when you want to create a new .xpi file, VS Code's Tasks are handy.
This here is a very simple task that uses 7-zip on Windows to create a .xpi:
{
"version": "2.0.0",
"tasks": [
{
"label": "Make Theme .xpi",
"type": "process",
"windows": {
"command": "C:\\Program Files\\7-zip\\7z.exe",
"args": ["a", "-tzip", "${relativeFileDirname}-theme.xpi", "${fileDirname}\\*"]
}
}
]
}
(this snippet uses variable substitution to read files and put .xpi file into specific dir)