Firebug is not working with Firefox version 50.0

Question

I am using Firefox 50.0. After auto update of Firefox to version 50.0, Firebug has stopped working and attempting to use it is showing an inbuilt Firefox console while inspecting any DOM element.

Is there any patch to use Firebug on Firefox 50.0 version?

Answer 1

Firebug does not work with multiprocess Firefox

The Firebug site claims that:

Firebug 2.0.18 is compatible with Firefox 30 – 52

However, it also explains that [emphasis mine]:

Firebug 2.0.18 fixes issue 8030. The extension is marked as multi-process (e10s) compatible so, it isn’t blacklisted and users can continue installing it. This way Firebug can help users to easily migrate into built-in Firefox developer tools – in case it’s running in multi-process enabled browser. When opened in a multi-process Firefox, Firebug’s tools cannot be used. Firebug will then only assist the user with migration to Firefox’s built-in tools.

They also direct you to read: Unifying Firebug & Firefox DevTools

That page says that [emphasis mine]:

Firebug 2 doesn’t work in multi-process browsers (i.e. e10s) and converting it is too complex, so it will stop working when e10s is activated in Firefox. You will be able to disable e10s for a while to keep using Firebug 2, but this won’t last forever.

The fact that Firebug does not actually work in multiprocess Firefox will account for different people having different experiences with Firebug working or not working in a particular version of Firefox. Firefox automatically enabling multiprocess mode will depend on multiple factors, including what other add-ons are installed in the profile.

Using Firebug in newer versions of Firefox

Thus, to use Firebug in newer versions of Firefox, you will need to disable Firefox from entering multiprocess mode. This can be done from the about:preferences page (also available from Tools➞Options). This an option which is under the "General" tab as "Enable multi-process Firefox ...". If multiprocess is not available, this option will not be shown. This option can also be changed by adjusting the preference browser.tabs.remote.autostart from about:config. [Note: browser.tabs.remote.autostart.2 and browser.tabs.remote.autostart.1 also appear to be used to indicate default states, thus I suggest using the about:preferences page to change this option.]

You can determine if your Firefox is currently running in multiprocess mode by looking in about:support. The line "Multiprocess Windows" under "Application Basics" will state if multiprocess is enabled or disabled.

Set up profiles explicitly for testing

Personally, I have different profiles set up for each of multiprocess explicitly disabled and multiprocess explicitly enabled (set browser.tabs.remote.force-enable to true), so I can perform testing under both conditions, with the state of multiprocess being enabled/disabled being known in advance.