I've been using the Firefox Command Line Interface (Shift + F2) to take fullpage screenshots in Firefox for several months now.
Below is the syntax I use to capture screenshots via Firefox's CLI:
screenshot --fullpage filename.png
However, upon upgrade to Firefox 54.0, anytime I attempt to take a screenshot of a webpage it now returns with "unknownError" almost every time. On a few occasions, I've gotten the error "TypeError: this.target.tab is null" instead.
I've tried taking screenshots of dozens of different webpages both with and without the --fullpage parameter with no success. In fact, the only screenshots I've been able to capture are of Firefox's "New Tab" page and other Firefox pages, such as "about:config."
I'd greatly appreciate any help. Thanks in advance!