If you have sync, and there is a problem anywhere, Shut Down Sync Immediately On All Devices to prevent the problem from spreading. Once the problem is fixed, perform the same repair on all computers/profiles before using sync again.

[v57+] Places Maintenance is built into Firefox.

Type about:support<enter> in the address bar.

You will find Places Database near the bottom. Press the Verify Integrity button.

When done, copy and post the results here.

this is the result from Verify Integrity:

> Task: checkIntegrity + The places.sqlite database is sane + The favicons.sqlite database is sane > Task: invalidateCaches + The caches have been invalidated > Task: checkCoherence + The database is coherent > Task: expire + Database cleaned up > Task: originFrecencyStats + Recalculated origin frecency stats > Task: vacuum + Initial database size is 15360KiB + The database has been vacuumed + Final database size is 15360KiB > Task: stats + Places.sqlite size is 15360KiB + Favicons.sqlite size is 15072KiB + pragma_user_version is 53 + pragma_page_size is 4096 + pragma_cache_size is -2048 + pragma_journal_mode is wal + pragma_synchronous is 1 + History can store a maximum of 19332 unique pages + Table moz_bookmarks has 1356 records + Table moz_keywords has 8 records + Table sqlite_sequence has 1 records + Table moz_annos has 601 records + Table moz_anno_attributes has 4 records + Table moz_items_annos has 0 records + Table moz_places has 20082 records + Table moz_historyvisits has 36330 records + Table moz_inputhistory has 194 records + Table moz_hosts has 0 records + Table sqlite_stat1 has 20 records + Table moz_bookmarks_deleted has 8 records + Table moz_meta has 5 records + Table moz_origins has 2408 records + Index sqlite_autoindex_moz_keywords_1 + Index sqlite_autoindex_moz_anno_attributes_1 + Index sqlite_autoindex_moz_inputhistory_1 + Index sqlite_autoindex_moz_hosts_1 + Index sqlite_autoindex_moz_bookmarks_deleted_1 + Index sqlite_autoindex_moz_origins_1 + Index moz_bookmarks_itemindex + Index moz_bookmarks_parentindex + Index moz_bookmarks_itemlastmodifiedindex + Index moz_places_hostindex + Index moz_places_visitcount + Index moz_places_frecencyindex + Index moz_historyvisits_placedateindex + Index moz_historyvisits_fromindex + Index moz_historyvisits_dateindex + Index moz_places_lastvisitdateindex + Index moz_places_url_hashindex + Index moz_annos_placeattributeindex + Index moz_items_annos_itemattributeindex + Index moz_bookmarks_guid_uniqueindex + Index moz_places_guid_uniqueindex + Index moz_keywords_placepostdata_uniqueindex + Index moz_bookmarks_dateaddedindex + Index moz_places_originidindex > Task: _refreshUI

Good.

Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

I started Firefox in Safe Mode. The Bookmarks bar was not displayed so I added back. Once I had it back I tried the folders, and they still behaved the same - opened once, then no longer opens

Let’s do a full clean re-install;

Note: Firefox comes in three or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.

Download Firefox For All languages And Systems {web link}

Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Note: Check Both Folders

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop

Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove any profile folders.

After rebooting the computer, run a registry scanner if you have one. Then run the installer.

If there is a problem, start your Computer in safe mode and try again.

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia