Like the Pearl Crescent folks, I'm an aficionado of being able to save web pages as they appear on the screen. One of the few times I've seen Mozilla actually listen to its users was when I reported Bug 293834, asking to have the Save feature save the current state of a page, including any text entered into fields, selected checkboxes / radio buttons, etc.; this was thankfully implemented (3+ years after my request, yes, but it was implemented, and without argument, something I've almost never seen on user requests since).
Fast-forward about 13 years, and my current favorite way to save web pages is using the Mozilla Archive Format extension, which saves to a single file, either in IE's MHT format, or MAFF, which is like Firefox's "Web Page, complete", but all in one ZIP file, which has lots of advantages, including saving disk space and simplifying file management. Sadly, Mozilla Archive Format is one of many must-have extensions that can't be ported to the new, crippled WebExtension framework. I'm not yet sure what I'm going to do once Firefox ESR drops classic XUL/XPCOM extension support in August of this year.
In any case, there are some pages that do not save successfully in HTML format, with or without Mozilla Archive Format. Printing to a file can sometimes work around this, e.g. using the Microsoft XPS Document Writer pseudo-printer, or printing to PDF on other platforms. However, some web pages stubbornly refuse to save properly in either of those ways, sometimes by design.
A good example is Google Books search result / sample pages. In the past, my approach to these was to use Alt + Print Screen to capture the browser window, but this is a bit of a pain since you have to run a paint program, paste into it, save from over there, and then quit that app. Another hassle is that if you're saving a window screenshot to report a problem to, say, a webmaster, by default your image is going to include any other tabs you have open and what button-presenting add-ons you're running, which may have privacy and/or security implications.
Pearl Crescent Page Saver bypasses both of those hassles and saves time in doing so, since it saves just the web content pane. At first I didn't think I'd use the Header and Footer options (especially since at first I worried they might obscure content rather than being prepended and appended to the image), but currently I'm using %t (page title) as my added header, and %u (page URL) as my added footer, which makes up for the fact that the browser's title bar (oh, yes, I still have one of those wrongly endangered beasts, being a Classic Theme Restorer user) and URL bar are not included in its capture images. Another great advantage Page Saver has over doing window screenshots is its ability to save an entire page as an image, not just the currently visible portion.
One problem case I was hoping Page Saver would solve is pages that you want to save while an element is visible that only comes up during a mouseover. An example is the Amazon listing page for an item I was buying that had a "1 Applicable Promotion" mouseover popup. When trying to save as MAFF, the popup would disappear when the save window came into focus. Since I couldn't mouse over to the camera button, I assigned a Page Saver keyboard shortcut (Ctrl + Alt + P). However, although the popup remained visible during saving, the screenshot produced is evidently not based on the dynamic state of the page, as it was missing the popup. A more serious problem was that after assigning a keyboard shortcut, the Page Saver functionality kept randomly activating when I wasn't pressing the assigned key combo, so I was forced to unassign it (and for this reason I reduced my rating from 5 to 4 stars). I guess for now in these cases I'll have to stick to the old standby of Alt + Print Screen plus a paint program.
It's good to see that there's a WebExtension port of this add-on, though it'd be nice if there were some documentation on which features couldn't be ported to the WE APIs. Looking at one of the screenshots, it appears that the header and footer options are unfortunately among those. Finally, it'd be nice if the documentation were updated to remove the stuff saying that certain features only work in the Pro version, which is apparently no longer sold.
I uninstalled the WE version, installed the classic XUL version, restarted the browser, re-logged into the Telegraph site, re-expanded and 'Load More'd the comments, and then captured the page. The PNG file was saved instantaneously, and properly contained the content that it was supposed to.
I was tempted to leave a negative review of Page Saver WE, but I know the developers are hamstrung by the ill-conceived WebExtension platform, so I'm just updating this review of the old, working XUL extension.