I am running Boostnote 0.10.0 on High Sierra 10.13.3. My broswer is Firefox Quantum 58.0.2 (64-bit).
Using the export to HTML feature renders some characters incorrectly. For example, the – character is rendered as either – or – , as seen here:

It looks like the  occur where  s are, as seen in the developer tools here:

In addition, apostrophes (') render as ’, as seen below:

In the developer tools, here is the same instance of isn't:

Attached is a note file and its HTML export that demonstrate the issue. I changed the cson and html file extensions to txt so GitHub would accept them.
403e979b9127baf0d473.txt
export.txt
_(I can't provide the exact file I noticed the bug on because it contains private information, but I am providing a heavily censored duplicate which shows the same symptoms.)_
EDIT: Another example is double quotes (") being replaced as well. "Internet of Things" is rendered as below:

Funny. 😂😂 I think it is because that we forgot to put <meta charset="UTF-8"> when exporting it.
Could you check again after put the meta tag to the exported html file?
Adding <meta charset="UTF-8"> to the exported HTML resolves the issue.
I've opened a pull request with a fix. ^
@thedavidgay Thank you for the contribution!
Most helpful comment
Adding
<meta charset="UTF-8">to the exported HTML resolves the issue.I've opened a pull request with a fix. ^