"Insert Text Or Mathematical Calculation into field" problem

I'm trying to uase the "Insert Text Or Mathematical Calculation into field" option under Conditions, but am having visibility problems regarding field selection (see theattached). Can you please help?  Thanks

Hello,

Thank you for contacting us.

I've cloned and tested your form and was able to see the option. Can you try it on a different browser and see if that helps.

You can also try to maximize the window.

The original screenshot is from Firefox and doesn't happen every time. The same thing is happening with IE. 

I would recommend you to use Chrome instead, this the most recommended browser to edit forms in our builder.

Thanks, but my users primarily use Firefox. Maximizing the window helped.

Glad to know that made the trick. Do not hesitate to contact us anytime for further help.

Thanks for all your help, now and in the past. Replies are always quick, helpful, and polite!