I'm not sure what that add-on is. Can you provide more information about it, for example, if you follow the "More" link for it on the Add-ons page, does it have a home page address that you could post, or could you copy/paste the description of what it does?

Sorry to hear about the crashes. If you are getting the Mozilla Crash Reporter form, your Firefox may have logged some data that would help track down the cause of the problem. You can submit that data to Mozilla and share it with forum volunteers to see whether it points to the solution. Please check the support article "Firefox crashes - asking for support" for steps to get those crash report IDs from the about:crashes page, and then post some of the recent ones here.

Also and/or meanwhile, could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any less crashy?

The add-on in question comes fromhttps://addons.mozilla.org/firefox/addon/checkcompatibility It comes from Fire Fox. Now what?

tommer22 said

The add-on in question comes from https://addons.mozilla.org/firefox/addon/checkcompatibility/

The description of what is does it very confusing. Are you enabling/disabling the extension as a whole, or going into its settings and enabling/disabling compatibility checking?? Either way, I'm not sure why this is affecting the stability of your Firefox.

Now what?

Were you able to find any crash report IDs and did Firefox work any better in Safe Mode?

It is possible that there is a problem with the file(s) that store the extensions registry.

Delete the extensions.* files (e.g. extensions.json, extensions.sqlite, extensions.ini) and compatibility.ini in the Firefox profile folder to reset the extensions registry.

• https://support.mozilla.org/kb/Profiles

New files will be created when required.

See "Corrupt extension files":

• http://kb.mozillazine.org/Unable_to_install_themes_or_extensions
• https://support.mozilla.org/kb/Unable+to+install+add-ons

If you see disabled or not compatible extensions in "Firefox menu button/Tools > Add-ons > Extensions" then click the Tools button at the left end of the Search bar to check if there is a compatibility update available.

If this hasn't helped then also delete the addons.json file.

Since it originated with Mozilla, I'd like someone there to explain how it became one of my add-ons and what use is it. Can I delete it? If so, how? No error messages appear, Flash seems to make FF lock up, and I have to close FF manually. Then when I re-open FF, I have to go to add-ons and activate "checkCompatability. Hope this helps, I dont know what else I can add.

All extensions are optional, none come with Firefox. Feel free to disable or remove any that do not seem valuable to you or which you do not remember installing. (You should always have a Disable button. If the extension is installed in a shared location, there might not be a Remove button.)

This is some standard guidance that addresses the most common issues with the Flash Player plugin. I'm sure you've seen some of it before, but just in case:

(1) If you have any recorders/downloaders that interact with Flash media make sure they are as up-to-date as possible, or disable them temporarily.

(2) Disable hardware acceleration in Flash: right-click the media in the player and choose Settings, then the first mini-tab and uncheck the box to use hardware acceleration.

More information in this support article from Adobe: http://helpx.adobe.com/flash-player/kb/video-playback-issues.html#main_Solve_video_playback_issues

(3) Disable protected mode (Windows Vista and higher)

The protected mode feature of the Flash player plugin has security benefits, but seems to have compatibility issues on some systems. You can disable it using the Add-ons page. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. On the right side, find "Shockwave Flash" and click the More link. Then uncheck the box for "Enable Adobe Flash protected mode" and try that for a day to see whether it helps.

See also:

• http://kb.mozillazine.org/Uninstalling_add-ons
• http://kb.mozillazine.org/Uninstalling_toolbars