The Advanced Search has a Before/After filter:

https://support.mozilla.org/en-US/search/advanced

or you can use Google or other engines with this query:

site:https://support.mozilla.org/ thunderbird my question

and click Tools to restrict the results to Any time, Past week, Past month, etc. and Custom range.

Thank you sfhowes. I tried using the advanced search to find my own post but had no luck:

I went to the Advanced Search Discussion Forums -- https://support.mozilla.org/en-US/search/advanced -- and typed in the title of my question, specified Created After 09/14/2020, and hit the Search Mozilla Support button. I got two results, neither of which was my question.

I then tried searching for the first line of my thread (using Ctrl-C, Ctrl-V) with same date specification and got the same results.

Interestingly, I also tried searching using google without success. In fact, I got the the following message: "Your search - site:https://support.mozilla.org/ thunderbird help by date - did not match any documents." I got more results by taking off the "https://support.", but still not much.

So what am I doing wrong? If I can't find my own question, how can I find other relevant questions?

All of your posts are found here, by clicking on your user name:

https://support.mozilla.org/en-US/user/DeElmo

I performed this search on Google and found several pages of results.

Yes, I know I can access my own messages that way (that's how I got here) -- I was just using my question for the advanced search because I knew it existed. Does the fact that I searched for my own question change the search results? I also did an advanced search for 78.2.2 without much luck.

Ah, I left out the slash before thunderbird. Still, when I clicked on your link and then specified a time frame of one month, I only got one page of results with only one en-us/questions result.