This issue has only been happening since the last update to 5.5.4.
Of note is that I have the tabbed browser setup so all windows are supposed to go into tabs rather than separate windows in Firefox.
When I hit the preview button and do not have my browser open at all (Firefox), it is opening 2 windows, one with my homepage and one with the preview. It should be opening both in the same window.
If I have a browser running or open and click the preview button, it adds the tab with that preview in it to the currently open window as it should.
Seems to be only happening when no browser window is open or running at all.
Also just tested, and it does not do this in Chrome so it’s something with Firefox browser that it’s not working right with.
I just tested this on my Windows 7x64 machine, and it did not do what you’ve described.
I set Firefox to my default browser and with no browsers open, I just clicked the Preview button on the website I currently have open in BSS, and it opened in a single tab in a single Firefox Window.
So whatever it is, it appears to be specific to BSS + Firefox on the Mac. Could be a number of things… the new Mac High Sierra OS, or Firefox on the Mac, or the combo of the two, or the last BSS update. I assume this didn’t happen with BSS 5.5.3 (or had you not yet upgraded to your new machine with High Sierra then?)
I guess if you’re really irked by it, the simplest test would be to temporarily downgrade BSS to 5.5.3, or temporarily downgrade Firefox to an earlier version, and see what happens (unless the devs see this first and have an answer.)
I think I scratch this issue as it just did the same thing when I opened a link from an email in Mac’s Mail program. I’m on MacOS Big Sur now so it’s probably something to do with that as well. Could be any number of things, but apparently it is not localized to only BSS. Might be a Firefox issue. I’ll go check their forums and see if anyone else is having this issue also. Thanks for checking.
If your options in firefox is set to Restore previous session then you always will have two tabs the previous session and the new link you opened