cannot unpin or edit a pinned tab

This is a followup to a previous post. I pinned a tab in firefox, and later deleted the webpage that was pinnned. I do not see a way to edit the pin, so I deleted it and created a new one with the new, updated webpage. I use the sync feature to keep all of my browser settings the same across three computers. I have tried multiple approaches to correct the problem. 1. turned off the sync and manually unpinned the tab, cleared the cache and browser history, checked to be sure I do not have the option to reload previous tabs turned on, booted in the mode that does not load any plugins, rebooted the computers 2. with sync turned off, after all of those steps, I opened the new page and pinned it on each computer. when I close the browser and reopen it on any computer, the original pinned tab returns. Turning the sync back on or re-enabling the option to sync tabs and history have no effect. Is there a way, even if it´s within the configuration files, to change that pinned tab or block the old one from opening? Note that the website for the old and the new pinned tab is the same. the difference is the page itself. the old tab was [website].administration-landing. the new page is [website].admin-lp. The is no reason why the old page, which no longer exists, continues to be pinned in the browser, but I can´t get rid of it. Please help. Thanks.