Separate Issue; Your System Details shows;

Installed Plug-ins

Shockwave Flash 23.0 r0 Shockwave Flash 22.0 r0
Having more than one version of a program may cause issues. You must remove the older programs. Then get the current full installer.

Flash: Grab the uninstaller from here: Uninstall Flash Player | Windows Uninstall Flash Player | Mac

Then reinstall the latest version.

Note: Windows users should download the active_x for Internet Explorer. and the plugin for Plugin-based browsers (like Firefox).

Note: Windows 8 and Windows 10 have built-in flash players and Adobe will cause a conflict. Install the plugin only. Not the active_x.

Flash Player Version: 23.0.0. 207 Flash Player (Linux) Version 11.2. 202.644

https://get.adobe.com/flashplayer/ Direct link scans current system and browser Note: Other software is offered in the download. <Windows Only>

https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download. <Windows Only>

See if there are updates for your graphics drivers https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

Is the problem just with Firefox? Does this happen with other programs? How often do you think this happens?

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. A small dialog should appear. Click Start In Safe Mode (not Refresh).

Is the problem still there?

"Is the problem just with Firefox? Does this happen with other programs?"

only with firefox

"How often do you think this happens?"

it varies depending on what sites are visited (I havent worked out which sites/scripts/whatever actually cause the problem), but on average once every 15 minutes

error does NOT occur in safe mode, however.

(also applied the flash reinstall as suggested above; not sure if that was suggested as a solution to the problem or as an aside)

Type about:preferences#advanced<Enter> in the address bar. Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Type about:addons<enter> in the address bar to open the Add-ons Manager. Hot key; <Control>(Mac=<Command>) <Shift> A)

On the left side of the page, select Appearance. Then select Default.

Now restart Firefox.

I am posting mainly as an easy method of following this thread, as we seem to have had quite a few similar questions recently.

As the problem goes away in Safe mode please test with all Firefox extensions disabled by using the setting button in the add-ons manager. setting them to [Disable] (That results in the enable button displaying). If that works try re-enableing blocks of add-ons until you figure out which one causes the problem.

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

Do you really need

• Expire history by days 1.2.1 https://addons.mozilla.org/firefox/addon/expire-history-by-days/

The Firefox developer that wrote that add-on points out it will likely cause performance issues with Firefox and is usually an unnecessary add-on. (I think there was demand for that add-on due to a feature revision in Firefox)