Okay, I need to make an apology. After some more hunting, I found in System Settings-Appearance an option under "GTK Styles and Fonts" to fix the scrollbar issue. The scrollbars no longer overlap the buttons, although I am still having a minor issue. It's visible in the attached screenshot. The left side margin of the thumb (using the term from the Wikipedia page on scrollbars) seems to get left behind when the thumb is moved. When the mouse pointer crosses the edge of the scrollbar then the margin catches up to the rest of the thumb. Again, this only seems to happen in Firefox and not any other GTK2 apps.
When I tested Firefox on a different Kubuntu computer via ssh, the scrollbars looked completely different, they appeared to be using the native GTK2 scrollbars. Will try to test it directly (rather than over ssh) later on.
As suggested, I tried a "Complete Removal" of Firefox via Synaptic, followed by a reinstall, but this failed to fix the issue.
Okay, I need to make an apology. After some more hunting, I found in System Settings-Appearance an option under "GTK Styles and Fonts" to fix the scrollbar issue. The scrollbars no longer overlap the buttons, although I am still having a minor issue. It's visible in the attached screenshot. The left side margin of the thumb (using the term from the Wikipedia page on scrollbars) seems to get left behind when the thumb is moved. When the mouse pointer crosses the edge of the scrollbar then the margin catches up to the rest of the thumb. Again, this only seems to happen in Firefox and not any other GTK2 apps.
When I tested Firefox on a different Kubuntu computer via ssh, the scrollbars looked completely different, they appeared to be using the native GTK2 scrollbars. Will try to test it directly (rather than over ssh) later on.
As suggested, I tried a "Complete Removal" of Firefox via Synaptic, followed by a reinstall, but this failed to fix the issue.