If you can't find it in the History itself, it is time for some detective work. Open up a terminal window and cd to your profile folder, something like
~/.mozilla/firefox/xxxxxx.default/. Open the places database:
If you don't have sqlite3, simply install it. Note:
sqlite3 is NOT the same as
Now Firefox distinguishes web pages from visits to that page. First, we look up the id of the offending page.
select id, url from moz_places where url like "offending url here";
If you don't know the whole URL but a significant bit of it, put it like this:
select id, url from moz_places where url like "%part-that-you-do-know%";
This will give you a number, let's say xxx. Let's find the most recent visit to that page:
select * from moz_historyvisits where place_id = xxx;
The first number on the resulting line is the number of your visit; the second number, call that yyy, is the visit to the referring page. So do:
select * from moz_historyvisits where from_visit = yyy;
This will give you a similar line. This contains the id of the page that led you to the offending page. The third number on that line is that id. Call it zzz. Now find the URL from that visit:
select url from moz_places where id = zzz;
And that gives you your URL.