You most likely cannot directly convert jsonlz4 to html, i.e. export Firefox backup to a HTML page. However, what most users are actually after is to recover the links saved in the backups.
The easiest way to achieve jsonlz24 to html conversion would be to restore the backup in Firefox and then just click on the bookmark to load the page. You can restore bookmark backups through the browsers bookmarking management option.
You can also use some of the recovery tools for this, for example the Firefox Bookmark Backup Reader/Decompressor.