Hello, Stuart.

I used Firefox 70 with BookMacster for 6 weeks and am now using Firefox 71.  Both of our extensions, BookMacster Sync and BookMacster Button, work fine for me.  (For syncing, you need only the Sync extension and for direct bookmarking, you need only the Button extension, but you can install both for special use cases.)  Our BookMacster Button shows an icon in Firefox' toolbar, but the BookMacster Sync extension does not – it works invisibly.

Actually, I thought it was several versions ago, in the Firefox 60s, that the default-beta profile was introduced.  When I run a beta version of Firefox, it uses the default-beta profile.  You'll probably also have a regular default profile.  Both of these will show in BookMacster's document tab > Settings > Clients, in the popup menu, as well as in the rows of menu > BookMacster > Manage Browser Extensions.  These two profiles have separate, independent bookmarks collections are also separate and independent as far as BookMacster is concerned.  You must be careful to select the desired profile when either setting Clients or installing extensions, to match the profile you expect when you run Firefox.  You can set either or both to be Clients and install extension(s) into either or both.  For the latter, be sure to follow the instructions and ensure that Firefox is running in the desired profile.

To determine which profile you are currently running in Firefox, enter about:profiles into the address bar, then look for the text This is the profile in use and it cannot be deleted.  This is wonky, but a vast improvement over finding the folder in about:support which is what we had until a year or so ago.  To change profiles, click Launch profile in new browser, which will launch another instance of Firefox – you'll actually see two Firefoxes in your Dock.  You should quit any Firefox running any non-target profile before installing an extension from BookMacster.