Hi,

Please check if this happens in Safe Mode. Safe mode disables the installed Extensions, and themes (Appearance) in Tools (Alt + T) > Add-ons. Hardware acceleration is also temporarily disabled - the manual setting is Tools > Options > Advanced > General > Use hardware acceleration when available. All these settings/options/add-ons can also be individually or collectively disabled/enabled/changed in Firefox normal mode to check if an extension, theme, option or hardware acceleration is causing issues. Disabling/enabling hardware acceleration, and some types of add-ons in normal mode may require a Firefox restart.

Uninstalling Add-ons

Uninstalling Toolbars

Troubleshooting Extensions and Themes

Problematic Extensions

Options

Thanks, dum, but as the problem occurs sporadically, it's going to be difficult to check its ongoingness via the means you suggest.

Hmmm. I guess what you're telling me is that the problem could be the result of extensions, themes, or options that are incompatible with FF 13--yes? But, if so, wouldn't others report the difficulty? Would reinstalling FF 13 help?

Thanks.

It could be a feature of an extension, or it could be a feature gone wrong. Hardware acceleration could also cause visual glitches. Usually all problems may not be universal and many cases could be unique to a particular configuration, or it could be the sum of various factors that may not be easily replicable in any other configuration. You can try a clean reinstall but it could be overkill and may not solve the issue if for e.g. acceleration is the problem. Another thing you could try is to use the default theme, and manually disable suspicious extensions and hardware acceleration.

Thanks, dum. I'll proceed as you suggested.