Fix Firefox (and other) applications that won't pin to Budgie panel

When running Budgie (under Solus and Ubuntu Budgie) I found that I am not able to right click certain applications and select the “Pin to panel” option.

The solution to this problem is identical to the solution I documented in another post: Fix missing application icon in Budgie panel.

The following are the steps to fix the problem for Firefox, if you need to fix other applications I suggest following the steps in the fix icon post.

Edit /var/lib/snapd/desktop/applications/firefox_firefox.desktop (you’ll likely need to use sudo).
Add the following on a new line under the [Desktop Entry] section then save:
```
StartupWMClass=Firefox
```
Finally, quit and restart Firefox, you should be able to right click the icon and see “Pin to panel” now.

If this helped you out or didn’t solve your problem, please let me know on twitter.