I had been using an old version of Firefox, because I have a legacy add-on which is incompatible with new versions. Now many websites have stopped working in the old version of Firefox, and this forces me to update to Firefox 56 and change the code of the legacy add-on to make it workable.
In general, the legacy add-on works in Firefox 56 but there are some problems that I have to solve.
My current problem: I change the add-on files in a text editor, save them, restart Firefox, but instead of using the new add-on files, the browser keeps using the old versions of these files. I have no idea where it keeps them.
I have disabled checking for add-on signing in the browser. The add-on code resides in a folder on a local disk (not compressed). In the Firefox profile, in the folder "extensions" there is a text file that contains the path to that folder. The browser loads add-on, the add-on works, but uses the old versions of the add-on files, even after I change the original files. I tried to disable and then enable the add-on, this did not help at all.
How can I force Firefox 56 to reload this legacy add-on after I change the add-on files?
Copy to a path the package (xpi) for installed and disabled/incompatible addon. (...\Profiles\xxxxxxx.default\extensions) Note that files can have names like {b9db16a4-6edc-47ec-a1f4-b86292ed211d}.xpi but using about:support you can find the name associated to this addon.
Edit install.rdf (contains extension identification and compatibility checks) to include a different version modify max version 56.*
Edit chrome.manifest (contains technical configuration which can be common for all browser and version or can be customized per each different web browser or version) Modify appversion to apply to your browser version
Add all files to a file.zip
You have more details in: best-practices-with-firefox-palemoon.html