If you use the Tab Mix Plus extension:

Try updating to version 0.4.1.9. To do that, you can use the Add-ons page. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then find the "gear" button above the list and "Check for Updates". Firefox will let you know if you need to restart the browser to complete the update process.

Does that work? If necessary, you can install the latest version from the Add-ons site: https://addons.mozilla.org/firefox/addon/tab-mix-plus/

If you do not use the Tab Mix Plus extension:

Could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

Sorry, let me give you the Mac versions of those keyboard shortcuts:

If you use the Tab Mix Plus extension:

Try updating to version 0.4.1.9. To do that, you can use the Add-ons page. Either:

• Cmd+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then find the "gear" button above the list and "Check for Updates". Firefox will let you know if you need to restart the browser to complete the update process.

Does that work? If necessary, you can install the latest version from the Add-ons site: https://addons.mozilla.org/firefox/addon/tab-mix-plus/

If you do not use the Tab Mix Plus extension:

Could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is not running: Hold down the option key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

You can check for problems with the places.sqlite database file (bookmarks, history) in the Firefox profile folder.

• Places Maintenance: https://addons.mozilla.org/firefox/addon/places-maintenance/

See also:

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox
• https://support.mozilla.org/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file

Thank you jscher for your trouble. I don't have Tab Mix Plus installed. I'll try starting in Safe Mode later today.

and thanks cor-el for the links to research.