You can try disabling the extensions. That does not un install them and may be sufficient to solve the problem. Start by disabling them all. If it then works ok re-enable 1/2 of them. You now know which 1/2 is the problem split that in 1/2 again until you find the problem.

• Disable or remove Add-ons_how-to-disable-extensions-and-themes

If the problem does not go away when all of the extensions are disabled the problem may be something else.

Post back with how you get on.

In Firefox Safe mode these changes are effective:

• all extensions are disabled (about:addons)
• default theme is used (no persona)
• userChrome.css and userContent.css are ignored (chrome folder)
• default toolbar layout is used (file: localstore-safe.rdf)
• Javascript JIT compilers are disabled (prefs: javascript.options.*jit)
• hardware acceleration is disabled (Options > Advanced > General)

• plugins are not affected
• preferences are not affected

No problem today...the scroll bar is back, even after I changed the minimum font size setting from "none" back to the size I prefer. I hope the problem has been solved, but I'll keep this problem line open until I'm sure it is solved.

2:35am ...and now the scroll bar is gone, changing the minimum font to none has no effect.

Does it help if you make the Firefox window wider?

Are you zooming pages?

• View > Zoom > Reset (Ctrl+0 (zero); Command+0 on Mac)

You can check for problems caused by a corrupted localstore.rdf file.

• http://kb.mozillazine.org/Corrupt_localstore.rdf

Do you have extensions that place content (information) on one of the visible toolbars?

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

• Do NOT click the Reset button on the Safe Mode start window.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes