Hi,
Can you post a screenshot of this? It will help understand what's happening.

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Thank you!
Michael

Thanks Verdi! Attached you can see the little Gmail icon tab behind my open Ask Liz tab. And although you can see it, it's not clickable.

Ok - it looks like you are using an add-on that changes the shape of the tabs. My guess is that this is causing the issue. The add-on author probably hasn't updated the add-on to take the new tabs into account. My suggestion would be to disable the add-on for now. You might also look for another add-on that provides features similar to the one you have now.

If you need them, instructions for disabling add-ons are here.

Hmm, I swear it was a new feature in a past firefox update and I even searched my addons and don't see anything related. I just right click the tab and it's an option. I did find an addon called pin/unpin and installed it to see but it does the same thing. Well hopefully it'll resolve in the future. Thanks!

Well guess what?! I uninstalled the addon "colorful tabs" as it wasn't working well w/the new layout and now I can pin tabs again! Phew :)

The tabs in your Firefox don't look like anything that is possible without an add-on or some modified hidden preference (so I don't think it will resolve in the future). Since it looks like you are using a number of other add-ons I would recommend trying to troubleshoot the issue by using safe mode. Instructions for that are in this article: Diagnose Firefox issues using Troubleshoot Mode

Ah - we were typing at the same time! I'm glad it's working now. :)