Version 3.0 works fine here!
With the new feature, which shows saved status of the page right away, now it is very easy to make a decision whether or not to save the page. To do this with prior versions, I had to first check the newest saved page and to see if it exists or not. The saving process is being done in background, so I can browse other pages while the add-on saves a page.

(Below is my review a year ago about previous version)
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Once worked fine, but for the past few months, it has got "Fail with status: 498 No Reason Phrase" error with Retry button, which fails all the time on firefox (waterfox as well). So, now this extension is quite useless and needs to be updated.