Even better, the option to set new tab to a webpage is gone. The only choices are the Firefox default page or a blank webpage.
Normally this wouldn't be a problem. I'd just try one of the dozen of known tweaks to about:config or userChrome.css and defeat this behavior. Except none of them impact this.
Again, this is only for a new tab.
FWIW, and as a workaround and not any sort of defense of FF breaking itself: You could, from an existing page, type what you want in the search box, then middle-click (or ctrl+click) the search button, which opens the result in a new tab. Again, you shouldn't have to do this, but it seems like it'd patch your workflow.
The action is a bit distracting but it happens fast enough that it's not a bother.
I'll note it was the 2nd extension I tried. It may be some onerous Firefox security measure needs to be bypassed & the first extension hadn't managed it yet.
I feel like default behaviour should be broadly helpful, while specifically helpful behaviour should be easily accessible but not so easily accessible that a mindless click triggers it.