Hello, smaziarz
Thank you for the clarification, From the "Firefox opening links to the wrong page" perspective, that is an error on their end, and you will need to reach out to mozilla to have them address the issue with their browsers navigation. The link is well formed and other browsers do follow it properly.
As for the issues with opening these items in our app. I have forwarded this report to the Dev team for review. I am unsure if the extended passthrough that is pushed to us includes this data and we are ignoring it, or if it is being stripped out by Firefox or Windows itself before we have a chance to act on it, but the Team will investigate and hopefully we can see a fix in a future build.
Somewhat related, You mentioned earlier that it "File opens to whatever the last page was you were viewing", This is a setting in the Editor, and even if we can fix this issue, if you do not change that setting, you will experience the same. Under the Editor Preferences (Ctrl_K), in the page display category, there is an option to "restore last viewed page and layout... etc". If you wish for any external links pointing to a file you have opened in the past to be respected, you will need to disable this option.
However, at this exact moment, this option only makes these html links open the file to page 1. So while this will not fix your issue at this exact moment, it will be required when a fix is available.
Kind regards,
