Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

A possible cause is a problem with the file places.sqlite that stores the bookmarks and the history.

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

I have read and tried all the advice I could find here but nothing works not even safe mode and I have no sessionstore files like suggested elsewhere here. My bookmarks work just fine so I don’t think that is the problem. It is only the Forward, Back and Reload buttons that don’t work.

You can still give a corrupted places.sqlite file a try and follow the instruction to delete all places files in the profile folder.
A corrupted places.sqlite file can cause such issues.

You can use this button to go to the Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder

OK, I have deleted all the places.sqlite files and restarted but navigation is still greyed out. I tried deleting them again and restarting in safe mode but it’s just the same.

Create a new profile as a test to check if your current profile is causing the problems.

See "Basic Troubleshooting: Make a new profile":

• https://support.mozilla.org/kb/Basic+Troubleshooting#w_8-make-a-new-profile

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If that new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

See:

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Right, I made a new profile and checked that the navigation buttons worked properly. Then I reinstalled all of my extensions e.t.c. two by two in case one of them was causing the problem and I configured them exactly as before. Would you believe it the navigation buttons remained working. I have no idea what was causing the problem in my previous profile but I suppose that doesn’t really matter as the problem has gone away. Thanks to everyone who helped. It is most appreciated.