Screenshot taken with addon: https://i.imgur.com/rgG0tMb.png Screenshot taken without addon: https://i.imgur.com/BV3sxqP.png
The zero length character is also at the end of the title in this hacker news entry.
The zero width characters might be leftovers from the transcription process, marking disagreements or known spelling errors or something.
If you click into one of the books on that website, you can see options to mark stuff as "ex" or "unc", which explains the weird markup (<span class="ex">er</span>).
> <div>you cant p<span class="ex">er</span>seve the suet from the meat</div>
It's also around a possible spelling error"? (preserve vs perseve)
See here for more on early modern "secretary hand" abbreviations: https://www.english.cam.ac.uk/ceres/ehoc/conventions.html#co...
EDIT: my bad, I assumed the earlier hn link there was about the discussion on fingerprinting with them.
For Firefox there is this extension that does search and replace based on regex (so you need to create the rule by yourself). https://addons.mozilla.org/de/firefox/addon/foxreplace/?src=...
Apply an autoload rule with these settings:
Name: zero length replacement
HTML: Output only
URL: <entering no url matches all sites>
Replace: (\uFEFF|\u200B|\u200C)
Type: Regular expression
With: <span style="background-color:#F00 !important">😳</span>