docs(devtools): adding firefox development documentation (#44952)

Adding DevTools documentation for Firefox.

PR Close #44952

devtools/docs/firefox.md

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+# Installing Angular DevTools in Firefox
+
+To install Angular DevTools in Firefox follow the steps:-
+
+![click on remote debugging](assets/firefox/step-1.png)
+Open menu item from top bar `Tools -> Browser Tools -> Remote Debugging`.
+
+![click on this firefox](assets/firefox/step-2.png)
+After clicking `Remote Debugging` click on `This Firefox` option from left navigation. You will see the below screen with list of extensions. Temporary extensions are unreleased extensions loaded in development mode.
+
+![load temporary add-on](assets/firefox/step-3.png)
+
+Click on `Load Temporary Add-on` button to select and load the Angular DevTools extension for Firefox.
+
+![select file](assets/firefox/step-4.png)
+Select any file from `dist -> shell chrome` directory to load extension. If you have not build extension for Firefox yet. You can do it using `yarn build:firefox` which will generate build for Firefox.
+
+![view extension](assets/firefox/step-5.png)
+After selecting file and clicking open, you should be able to see Angular DevTools as a Temporary Extension in Firefox.
+
+![test extension](assets/firefox/step-6.png)
+Open any Angular application in dev mode and open Firefox DevTools you should see Angular Tab in there.