(Yes, I know that there is a thread about this, but given its length which would take a long time to search, with no promise of that being useful, I'm going to post this.)
[Corrected text: I had written "icon", but the extension specifically refers to a toolbar button, and that is what is missing.]
Windows 11 Version 21H2, (OS Build 22000.493); Firefox 97.0 (64-bit); Forecastfox (fix version) Version 4.26
The button has been at the far left end of the Bookmarks Tool Bar for an unknown length of time; it was there late yesterday afternoon, has since disappeared and I cannot find it.
i have run Fx in Troubleshooting Mode, I have removed the extension, restarted Fx, reinstalled the extension, have opened the Fx Bookmarks Manager, have done an on-line search for information, and so far have had no success in finding the wayward button
I could post a Missing button poster at our branch library, to go with a few of USPS Package Tracker emails for packages that don't exist, even one that stated that a package was out for delivery four days after we received it, all to no avail I am sure.
If any one has a spare button for this extension, or could tell me where to find my own button, that would be nice.
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Later: I created a new Fx profile, opened it, installed Forecastfox (fix version), where the toolbar button is also missing. I wondered if a Windows Update might have caused the loss of the button, but there were no such updates until after the button disappeared. I have sent an email to the author, who unfortunately lives in Kyiv, Ukraine. I would not have been surprised were my email bounced back, but after some four and one-half hours, it has not, but it still might do so, or the author may not be able to reply.