Firefox - Shortcut does not work when developer tools panel is active

Currently it is not possible to reload CSS using this extension when any of the Firefox developer tools is active. Here's the flow which is severely affected by this issue.

1. Open web page
2. F9 to reload CSS
3. Inspect an element to change its CSS
4. Alt + Tab switch to editor and change CSS
5. Alt + Tab switch back to firefox and press F9
6. CSS should reload but nothing happens

The workaround

after (5) above, click the element (or anywhere on the page), and press F9 to reload CSS.

Start by reproducing the numbered flow in Firefox with developer tools active, then locate the extension's shortcut handling. The issue names no files or tests; done means F9 reloads CSS after returning from developer tools without first clicking the page.

Written by the indexing model from the issue text.