I have done a search for the term "firstborn" in the OT in the ESV and have 132 results. Is it possible to save them all in one go to an excel spread sheet?
Not to my knowledge... Well I guess it all depends on what information you want saved in the spreadsheet.You could add all 132 (or however many) resources to a collection, and export the bibliography in a .csv file which Excel can open. But thats not going to have the search results, just the bibliographic information.
Yes, it's pretty easy.
From the panel menu of the search results (click the search icon to drop it down), choose Print/Export...
Then under click "Send to new document" click "Microsoft Excel"
Here's what the result looks like:
If you don't want the ESV "X" column and/or the Text column, you can delete them in Excel.
Is that what you were looking for?