Hi, please try a Refresh but Note that this does more than uninstalling and re-installing does. Normal uninstalling does not remove some preferences which may have become corrupt. Please Refresh but do this 1st: Delete your Cookies and Cache and TEST.

• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

then

• https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

Please let us know if this solved your issue or if need further assistance.

Thanks for the reply, but the instructions don't do the job. The setting to disable the "Page Preview" feature doesn't remain in effect once I quit from Firefox. The next time Firefox is opened, the Page Preview feature needs to be re-disabled. Somehow that setting is not being saved in in my profile?

Maybe it's because I use Windows, but I can't tell what feature you are turning off.

Is this related to the "Firefox Home" or "New Tab" page that has a number of different categories of content including sites from your history, recommendations from Pocket, etc.? Changes to your settings for those pages are saved in a file named prefs.js and this article is probably the most relevant to problems with that file: How to fix preferences that won't save.

Or is it something else? Maybe a screenshot would help me... or maybe another Mac user would instantly know what it is.

Per the request for screen shots, I've attached an image showing one of these "Page Preview" windows, as it appears in Wikipedia. You'll notice the little "gear" icon in the lower right corner. Clicking on that produces the dialog box in the 2nd attached image. This is the enable/disable setting I'm wondering about. I click on the "Disable" button, click on "Save", and another dialog box appears, in which I click on "Done". All well and good then, in the current Firefox browser window, but it doesn't persist.

Part of the problem is, of course, determining what the particular setting might be named. I don't know how to determine that, unfortunately.

Oh, I never noticed that before. That is a feature of the MediaWiki platform, which is the server software for Wikipedia and various other "wiki" sites. If you set Disable, the site saves a flag in Local Storage, which is a type of storage scripts can use which Firefox manages similarly to cookies.

The attached screenshot shows where a value is saved if I choose Disable. (In the Storage Inspector tool.)

If you clear Wikipedia cookies , that might also explain the Local Storage being cleared.

This being a MediaWiki thing explains it. I have Firefox set up to clear cookies, cache, ect., each time it's shut down. It's no surprise then that the Page Preview setting doesn't persist.

Thanks for your help!

I don't know of any add-on for this, but in theory an add-on (or a userscript) could set the local storage value automatically when you visit the site. I guess that would be worth investigating if you close out Firefox frequently.