First of all ad blockers are not crap.
You are better off to keep them activated and disable only when you know that a trusted source is asking you to do so.
Unfortunately there is no 'one fits all solution' here.
You need to find out what ad blocker is enabled in your Firefox.
Goto Tools, Add-ons, Extensions or try keyboard shortcut ‘Ctrl + Shift + A’ and find the ad blocker that has a button with Disable and click in it. It should toggle to Enable, which means it is disabled but ready to enable again when you need it.
Alternative there might be a slider switch to disable/enable.
Some ad blockers might show a small icon, usually top right of your browser, when you mouse over it it show the ad blocker. Click on it while you are on the yahoo website and it might show something like 'disable ad blocker for yahoo only'. That would be the best solution.
Another thing that might be causing problems is blocking Popup Windows.
That can be disabled in the Firefox Preferences, Privacy & Security, Permissions, untick 'Block Popup Windows'
But do this only if the ad blocker disable thing didn't work.
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