Sounds like an issue with Malwarebytes and for their support.

Hi, if you haven't already, please try doing a normal shutdown and restart of your system You need to make sure Malwarebytes is not locking any Firefox files so Firefox can access them normally.

Any improvement?

Sometimes a bookmark restore will fail due to a problem with the "Places" database. Could you let us know what you get when you run the "Verify Integrity" function. That's here:

Open Firefox's Troubleshooting Information page using any of these methods:

• "3-bar" menu button > "?" Help > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter/Return

Near the bottom, there is a section titled Places Database -- that's the file which stores history and bookmarks. Click the button labeled Verify Integrity. There may be a 10-15 second delay before results appear.

If all is well, the report that appears below the button should start with:

> Task: checkIntegrity
+ The places.sqlite database is sane
+ The favicons.sqlite database is sane

Does yours say that, or something else? You can select and copy the report, and then paste it into a reply for review and comment.

I "solved" the issue by using "R and shift" and reinstalling from an earlier date, i.e the day before. This appears to have reinstalled bookmarks and toolbar without my having to do any complicated fault tracing, etc!! I tried most everything else (but admit the last instruction set was too difficult-for now)...apart from restarting, trying Firefox import from an earlier date, which did not work, trying to import from HTML (fail) and most of the other trickery, the question is whether my 10 year old Macbook Pro is giving up the ghost (i.e have had intermittent frozen cursor on screen).

  Malwarebytes doesn't reply b/c of holiday weekend, but I'm pretty sure they, like Apple support, are going to say their system doesn't take away whole bookmark areas of browsers b/c "It takes a 'picture' every 24 hours and that's all".  I dunno if its them or a dying mac on my hands, but I'm going to uninstall it from that computer.

  One last question for now: I was under the impression that Firefox 'sync' should have reinstalled all my bookmarks, since they are shared between at least 3 of my Macs....wouldn't the failure of this as a solution suggest what one Apple support person said was "probably a permissions issue"?

I was under the impression that Firefox 'sync' should have reinstalled all my bookmarks, since they are shared between at least 3 of my Macs....wouldn't the failure of this as a solution suggest what one Apple support person said was "probably a permissions issue"?

Sync should keep the bookmarks between the 3 Macs the same. All of the different failures point to a likely problem with the Places (or site icons) databases. That was why I suggested trying the Verify Integrity feature as the first step. The potential next step after that would be to refer you to the following article, but I don't think you need it at this point if the error went away: Fix "The bookmarks and history system will not be functional" error message.