Try downloading the Yesware add-on from here.

Does the add-on re-appear?

If the above doesn't help, check with Yesware support, per this page: What do I do if I installed Yesware but it isn't displaying in Gmail? : Yesware

FireFox popup window "won't allow access to Yesware". When I click on "Allow" another popup appears immediately "can't connect to www.yesware .com"

When does the above error message appear?

Hello,

In order to better assist you with your issue please provide us with a screenshot. If you need help to create a screenshot, please see How do I create a screenshot of my problem?

Once you've done this, attach the saved screenshot file to your forum post by clicking the Browse... button below the Post your reply box. This will help us to visualize the problem.

Thank you!

You may want to (when doing the screenshot), ensure that your emails are not visible.

Here's the process: 1. go to Yesware.com 2. Click "download" 3. FireFox pop-up: FireFox prevented this site (www.yesware.com) from asking you to install software on your computer. 4. Clicked "Allow" 5. Immediately got another pop-up: The add-on could not be downloaded because of a connection failure on www.yesware.com

I don't know what I did (or didn't) but Yesware downloaded this morning and I was able to install it (after getting new version from Yesware). Thanks for your help (and quick response).