Correction. The ZOOM level for a site is not saved even within a browsing session. If I open a site, set the ZOOM level, close the site & re-open it immediately it has lost the ZOOM level.

In case you are using "Clear history when Firefox closes":

• do not clear the Site Preferences

• Tools > Options > Privacy > Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" > Settings
• https://support.mozilla.org/kb/Clear+Recent+History

Note that clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, and passwords.

You can rename the content-prefs.sqlite file to content-prefs.sqlite.old (or delete the file) in the Firefox profile folder to reset the page zoom for all websites.

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

• http://kb.mozillazine.org/Profile_folder_-_Firefox

See also:

• Default FullZoom Level: https://addons.mozilla.org/firefox/addon/default-fullzoom-level/

• http://kb.mozillazine.org/Zoom_text_of_web_pages
• http://kb.mozillazine.org/browser.zoom.full
• http://kb.mozillazine.org/browser.zoom.siteSpecific

• http://kb.mozillazine.org/toolkit.zoomManager.zoomValues

• http://kb.mozillazine.org/zoom.minPercent
• http://kb.mozillazine.org/zoom.maxPercent

Hi Cor-el.

I don't clear site preferences, and ZOOM is not remembered even within a browsing session. I have deleted the content-prefs.sqlite file, this made no difference.

From the links you gave me it appears there may be a hidden way of disabling FF site specific ZOOM, maybe this is what NO SQUINT has done?? This refers to a very old version of FF though, and there is no hint as to how to reverse it: https://bugzilla.mozilla.org/show_bug.cgi?id=419609

I don't want to install any more add-ons, I just want to restore the native FF21 site specific ZOOM functionality.

Thanks Petef

Make sure that you do not run Firefox in (permanent) Private Browsing mode.

• https://support.mozilla.org/kb/Private+Browsing

• Tools > Options > Privacy > Firefox will: "Use custom settings for history"
• Deselect: [ ] "Always use private browsing mode"

I'm not

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from an existing profile to the new profile, but be careful not to copy corrupted files.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Safe Mode made no difference.

In the end I got so fed up I restored all Mozilla Firefox directories from a 2 day old disk image backup (before No Squint was installed). Firefox ZOOM functionality returned, ZOOM level for specific sites now retained. This despite ALL Tools>Options being exactly the same.

Begs the question - what is the NO SQUINT add-on doing that seems irreversible even when it is removed??

Problem solved for now. I shall be more careful before I install add-ons in future. Thanks for your help Cor-el.