Please check the following article:

Search bar - add, change and manage search engines on Firefox

You can also loook through available search engines in Tools > Add-ons - I checked, but could not say for sure if the desired search engine is among available alternatives.

Hello Smo thanks for trying to help me. I had already tried the Search bar etc - tried everything I could under that heading but there was no help there whatsoever. All I can guess is that the McAfee Secure search engine is now incompatible with the Firefox browser because I've checked Firefox's add-ons again and there is definitely no McAfee Secure search engine. What I do know is that since the Firefox update I now have search engines that should not be showing, i.e. Amazon, Ebay, Twitter and Wikipedia - I don't use twitter so i definitely could not unwittingly download their search engine to my computer. I think Mozilla Firefox should get involved with my problem but do not know who to contact there and they haven't been forthcoming so far on their mozilla support page. Thanks again Smo.

1. Is that McAfee extension enabled in Addons > Extensions?
2. Check with McAfee for an updated version of their Firefox Add-ons.

Hi to the-edmeister. Just checked my emails. McAfee Secure Search engine is not a Firefox add-on. Only McAfee Site Advisor is showing in Add on Extensions. Just come off the phone to McAfee - nearly an hour! So you can guess the technician was very thorough. He is sure there is no problem with my computer and that Firefox updating is the cause of the missing McAfee search engine. There is no way to adjust the two search engine boxes that I now have so I'll just have to remember not to use the top box if I want to feel as secure as I did before. Hope you can understand the above (from a novice in computer wizardry!). Thanks for your assistance.

IMO something just ain't right there. If McAfee is adding a Search Bar / toolbar underneath the default Search Container (on the Navigation toolbar), either an extension or plugin should appear in Add-ons. External programs (whether they are security programs or are malware) aren't allowed to hide their Add-ons.

You can "hide" almost anything that appears on toolbars, by dragging it into the Customize palette.
https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars

Thanks edmeister for your help. I don't think I made things clear. I've checked the customer firefox etc and diagram of toolbars that you showed in your reply. My problem lies in the navigation toolbar where the search box is. In this box i searched with either the Yahoo or McAfee search engines (the McAfee search engine is part of McAfee Site Advisor which is included with the McAfee security package) - only Yahoo is now showing. When I first installed McAfee and its Site Advisor, its search engine became one of the search engines in the navigation toolbar, however, when I had to re-instal Site Advisor, its search engine was placed in the toolbar at the bottom of the firefox window, i.e. the add-on bar but only McAfee Site Advisor shows in my Add on/Extensions, not their search engine.

hello, it might be due to http://mike.kaply.com/2013/05/13/more-major-changes-coming-in-firefox-21/

when you go to your firefox program folder, which usually resides in C:\Program Files (x86)\Mozilla Firefox\ does it have a \searchplugins subfolder with a .xml file that relates to mcafeee search in it? if so, please move that to \browser\searchplugins instead...

Afternoon Philipp thanks for helping me. Very interesting and useful article on Mike Kaply. I've found the searchplugins subfolder which showed Blekko and McSiteAdvisor (XML Doc) - don't know why Afee is missed out after Mc. I've deleted Blekko in the hope of easily moving McSiteAdvisor to the searchplugins subfolder under browser but you know what? I can't find how to move it!! That's how much I know about computers. Can you please assist for a 2nd time. Thanks in advance.

ok, while you're in the \searchplugins subfolder, click on the McSiteAdvisor.xml file to highlight it & the press Ctrl+X in order to cut the file. afterwards go into \browser\searchplugins & press Ctrl+V which should paste the file into the right folder...

Sorry philipp, the McSiteAdvisor, which shows as an XML file 2Kb, will not cut. When I pressed Cntrl and X together there was a pinging sound - computer definitely didn't like this command. Any other suggestions for cutting it? Thanks again.

you may need to have administrator privileges to write into the program folder. go into the start menu, type explorer, right-click the Windows Explorer program icon & choose to run it as administrator. in the explorer-window that opens, then try to perform the steps mentioned above again... also make sure that all instances of firefox are closed while you're doing this!

You're too quick for me philipp. I'm going to be long winded in my reply, sorry but it's the only way i know to let you know exactly what I'm doing. Tried to perform the above steps - a box came on screen "do you want the following program to make changes to this computer - program name Windows Explorer. I clicked yes - new box appeared showing, among others, computer compaq (c), double clicked this then program files x86, mozilla, search plugins then highlighted McSiteAdvisor and pressed cntrl + X - it didn't disappear so I went back into Mozilla-browser-searchplugins and pressed cntrl + V. A box came on screen "File Access Denied - you'll need to provide administrator permission to move this file McSiteAdvisor". Three small boxes 'continue' 'skip' and 'cancel' are below. I've not clicked any yet as I don't know what I'm doing! H E L P.

Please provide a screenshot of your Firefox browser.
https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem

It is best to use a compressed image type like PNG or JPG to save the screenshot and make sure that you do not exceed a maximum file size of 1 MB.

Then use the Browse .... button below the Post a Reply text box to upload the screenshot.

Correct or not correct?
McAfee adds its' own search bar to the McAffee Toolbar, which is part of the McAffee Site Advisor extension.
So, you then have two separate search bars?

If the same search engines don't appear in both search bars, I would say that McAffee wouldn't be using the \searchplugins\ folder in the Profile folder.
Search engines added to Firefox after a Profile is already in use shouldn't be in the \browser\searchplugins\ folder. If they were added to that folder every new Profile created afterwards would have the new search engine, for every login user account on that PC which uses that Firefox program installation. That isn't the way Mozilla designed things to work; anything added by a user to "their" Firefox installation (Profile) goes into the "Profile" - not program files. And if you don't yet have a \searchplugins\ folder in your Profile, you haven't added a search engines just yet.

I would be very surprised if an extension would use, or would be allowed to install a plugin into the \searchplugins\ folder in either the program files or the Profile folder.

Hi edmeister I don't think I made my reply clear. McAfee Security suite was already installed on my computer. I then downloaded McAfee Site Advisor, which included (already ticked to instal) McAfee Secure search. I then had some problems with Site Advisor and was advised to delete it and reinstal - at this point I made the mistake of unticking the Secure search box and, you've guessed it, the Secure Search engine didn't instal. I had believed the Secure search would remain on my computer as I was only deleting Site Advisor! I'm wondering now whether I should remove the McAfee Security suite in its entirety and hope this removes the additional search box. If only I was a computer geek! Thanks for the link, only hope the screenshot comes through. will send after this as my computer crashed before - over maximum?

Here's the screenshot.

That screenshot shows a lot that wasn't mentioned. There are two Search Bars or "containers". It also shows that the McAfee "toolbar" ended up in the Add-on Bar, instead of where we normally see it, above the Bookmarks Toolbar.

I am confused as to why McAfee would add a Secure Search engine to the default Search Bar and also install its' own Search bar / box / container

The McAfee search box or container at the bottom of the browser window on the Add-on Bar shows Secure Search - does that work to do McAfee secure searches?
If it does, I wonder why a user would want or would need the Secure Search search engine in both Search Bars. Especially since McAfee since McAfee provides its' own Search Bar.

Thanks for your reply edmeister. Hope you received my reply posted just before my screenshot. I've been trying to explain that I now have two Search Bars (or boxes - if you mean, top right Yahoo and in add-on bar McAfee Secure search on screenshot?). I'm sure I don't have a McAfee "toolbar" and I should only have one default search box at top of screenshot. The small McAfee 'box' bottom right is part of the McAfee security package and has always sat in the add-on bar. Your 2nd para - I'm just as confused. All I know is that when I first installed the McAfee Security suite and their McAfee Site Advisor, their Secure search engine was added to the list of search engines in the default search box. It's only when I had to re-instal it "as an extra as explained in an earlier reply" that a new search box was installed. No-one seems to know how to remove this Secure Search box from the add-on bar. Looks like I'd better fully remove the McAfee security package and re-instal (and keep my fingers crossed) then I won't take up yours or anyone else's valuable time. Thanks. thanks. thanks for all your assistances.

That McAfee stuff sitting in the Add-on bar has what appears to be 3 separate elements; the McAfee logo (which is probably some sort of control button), the Search container (with Safe Search showing), and a green "advisory" button. IMO, when an extension adds 3 elements which are joined together (or placed then at the same time {during installation}) that makes for a "toolbar", even if it is placed or is sitting on another "toolbar".

Chances are reinstalling that McAfee add-on may not "fix" anything; an extension's preferences and settings usually don't get removed when the extension is uninstalled. So when the extension is reinstalled, all the former setting (and faults) are still there.

Evening edmeister. It's almost 7pm but still almost 80 deg Fahrenheit (I'm too old to do Celcius). Too hot to work, been taking the sun. Your replies get more and more interesting and informative but I don't know what IMO means. In the add-on bar - the McAfee logo would normally sit at the left hand side of the default search box (as Yahoo in the screenshot) to indicate I'm using McAfee Secure Search If I click on that McAfee icon it would take me to McAfee Site Advisor which gives me info about Secure search. The green boxed McAfee Secure is another part of Site Advisor which confirms the link or page I'm on is safe to use. Hope I'm not telling you something you already know. I really don't know why I have this problem, it's just disconcerting sitting in the wrong place. Later in the week I'll remove the McAfee security package in its entirety and let you know if it works. Thanks for your grand efforts and time on my behalf.

To The Edmeister, forgot one detail, I use noscript - the options regarding whether to allow all scripts used to sit in the add on bar, however when I visit a webpage now that informagtion is in a bar on its own directly below the toolbar "Most Visited, Getting Started, etc". Weird!