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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!

  • Same here. But even the about:config page screenshot is limited to the visible area. – DK Bose Jun 15 '17 at 4:23
  • On one laptop, I have Firefox 54 direct from Mozilla. On that, the screenshot doesn't work. On another laptop, which has the version supplied by the Ubuntu repos, it works fine. – DK Bose Jun 15 '17 at 11:09
  • I'm using the version supplied by Ubuntu. AFAIK the only difference is the Ubuntu Modifications extension, which I've had disabled for years. – PC_LOAD_LETTER Jun 15 '17 at 12:45
  • I also managed to find a bug report regarding this issue on bugzilla, indicating it was present in 53.0 as well. However, it worked fine for me in FF 53.0. bugzilla.mozilla.org/show_bug.cgi?id=1361110 – PC_LOAD_LETTER Jun 15 '17 at 12:48
  • I'm having the opposite problem: the CLI will still take a screenshot fine, if I can open the CLI in the first place. Most of the time I press Shift and F2 and nothing happens. Occasionally it deigns to open. – TRiG May 16 '18 at 14:17
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It seems things may have changed... This is what I did:

First select Tools > Web Developer > Inspector.

Look for the little cog-wheel with Toolbox options as its tooltip. Click on the cog-wheel to open the Toolbox options.

Scroll down to Available Toolbox Buttons and look for "Take a screenshot of the entire page". Check its box. A little camera icon should now appear to the left of the Toolbox options cog-wheel. If you don't see it, close the Inspector window and reopen it.

Firefox full page screenshot

  • Nice find! I know they've been developing a more fully featured screenshot tool for some time, planned for a later release. – PC_LOAD_LETTER Jun 25 '17 at 19:30
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    I managed to find a way to enable the feature in about:config by changing "extensions.screenshots.system-disabled" to "false." A "Take A Screenshot" button will appear in the upper right hand corner of the browser. – PC_LOAD_LETTER Jun 25 '17 at 19:31
  • However, I like your solution better, as it's quicker and doesn't entail automatically uploading all screenshots to FF servers. Hopefully the CLI screenshot feature isn't being deprecated, as I like being able to set my own filenames. – PC_LOAD_LETTER Jun 25 '17 at 19:31
  • @PC_LOAD_LETTER : I do not see "extensions.screenshots.system-disabled" in about:config in my version of Firefox. I posted a separate question to address that at: askubuntu.com/questions/1065359/… – bgoodr Aug 14 '18 at 17:25

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