improve Readme on how to run on Firefox

README.md

@@ -23,7 +23,31 @@ https://user-images.githubusercontent.com/1653275/149637382-65d50a85-fe30-4259-b
 
 * [Firefox Add-on](https://addons.mozilla.org/en-US/firefox/addon/nos2x/)
 * [Chrome Extension](https://chrome.google.com/webstore/detail/nos2x/kpgefcfmnafjgpblomihpgmejjdanjjp)
-* `git clone https://github.com/fiatjaf/nos2x && cd nos2x && yarn && yarn run build` then load as unpackaged on chrome://extensions with "developer mode" enabled
+
+## Develop
+
+To run the plugin from this code:
+
+```
+git clone https://github.com/fiatjaf/nos2x
+cd nos2x
+git checkout chromium                       # or git checkout firefox
+yarn                                        # or use npm or pnpm
+yarn run build
+```
+
+then ...
+
+* Chromium:
+  1. go to chrome://extensions
+  2. make sure, "developer mode" is enabled on the top right
+  3. "Load unpackaged"
+  4. select the `extension/` folder
+* Firefox:
+  1. go to about:debugging
+  2. "This Firefox"
+  3. "Load Temporary Add-on..."
+  4. select any file from the `extension/` folder
 
 ## Screenshots