Firefox has a setting for what appears in a new tab, but because add-ons can change or override the setting, the first step is to check for and either disable or remove any add-on that might be related.

On the following tab, I suggest disabling ALL nonessential extensions (by nonessential, I mean you can work for 24 hours without them):

orange Firefox button (or Tools menu) > Add-ons > Extensions category

Then restart Firefox.

Next, here are the steps to set a new "new tab" page:

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the filter box, type or paste newtab and pause while the list is filtered

(3) Double-click the browser.newtab.url preference and enter the desired value:

(i) Page thumbnails (default)

about:newtab

Or you can right-click > Reset the preference to restore it to default

(ii) Blank tab

about:blank

(iii) Built-in Firefox home page

about:home

(iv) Any other page

full URL to the page

Press Ctrl+t to open a new tab and verify that it worked. Fixed?

If you find that doesn't stick between Firefox restarts, there are a couple other things to check.

I had the same problem and solved it once with about:config. Until I reinstall FF to fix the icons and it began all over again. But I think I solved it once again. I checked the addons and there was one I´m pretty sure I didn't install : SearchNewTab 1.0. I removed it and now the stupid helpmefind didn't show anymore. Now I want to know how that crappy addon ended up in my FF. I will share my experience in the reviews of that addon.

PD I couldn't find it in the list of addons. Most likely it was Vaudix which installed it in my computer. I wanted to watch an old movie online and I had to install that exe. Silly me,right? Lesson learnt: never ever watch a movie online if they want you to install crappy things before.

SearchNewTab 1.0 doesn't appear in the official addons website, so my guess is that it tagged along with something else you installed. And that "something else" is still installed on your PC.

The edmeister, you're right. I´ve just edited my previous answer with a PS and then I saw your answer. As I said, it was a remnant of Vaudix. It was the cost of watching The Big Sleep online. And it didn't worth the nuisance.