doesn't work with apostrophe

That’s quite odd. The plugin should work fine with the apostrophe character. I’ve tested it some on my own site. Could you give me a little more info on how you’re entering content? Are you using the default WordPress content editor? Do you have any other plugins active that are adding items to your post content? That could be things like social sharing plugins that add social links above or below content. Are you using a theme builder of any kind like Divi or Visual Composer?

I’ll delve into the code a little too and see if there’s anything I could add to escape those characters and return them properly to hopefully prevent interference from other plugins too. You’re best bet may be to deactivate other plugins one by one and see if it renders properly to determine if there is a conflict. Not ideal, I know, but it helps me pinpoint what could be causing the issue.

I had the same problem so I made a fix:
change line 76 from this:
$footnoteContent = "<span id='easy-footnote-".$this->footnoteCount."' class='easy-footnote-margin-adjust'></span><span class='easy-footnote'><a href='".$footnoteLink."' title='$content'><sup>$this->footnoteCount</sup></a></span>";

to this:
$footnoteContent = "<span id='easy-footnote-".$this->footnoteCount."' class='easy-footnote-margin-adjust'></span><span class='easy-footnote'><a href='".$footnoteLink."' title='".htmlspecialchars($content, ENT_QUOTES)."'><sup>$this->footnoteCount</sup></a></span>";

hope it would help someone ??

I implemented your htmlspecialchars fix in the latest version. Thanks!

Thanks a lot you all.

Glad I could help ??