I'm not aware of a way to flag words that contain numbers.

Do you want to be able to add such mixed word to your personal dictionary?

Do you mean you have a list of specific strings (like part numbers) you want to validate against, or you want to flag any "word" that has a mix of letters and numbers?

I think an add-on or user script could do the checking, but displaying it is trickier: a plain text entry box like this one wouldn't allow underlining. Either way, I don't know of one off the top of my head.

Thank you both for the replies. I am looking for an addition to Firefox's built in spell checker which identifies and underlines spelling errors. I am proofreading OCR text on Wikisource/Wikipedia and I need to correct them.

I assume you are working with the texts in an editor. What kind is it?

• rich text editor - editable HTML like a webmail composition pane
• plain text editor - no actual formatting appears, but you can use wiki markup

It's a plain text editor with wiki markup. I included a screen shot.

Hmm, it's sort of a worst case scenario for a user script.

What a script might be able to do is create an overlaid contenteditable HTML element, populate it with the text, mark it up, then after edits are made, insert the unformatted textcontext back into the textarea.

jscher2000 thanks again for your interest. I am using a friend's very neat Regex .js script which scans the text and highlights such errors in preview mode, before saving. If you are interested, here is the link: https://en.wikisource.org/wiki/User:I.../typoscan.js

But, user scripts which are not integral to the Wikimedia software, need constant modification to comply with the bi-monthly modifications made to the core wiki software.

So, I was looking for another solution which is part of the browser, rather than the wiki software. I was just wondering how the installed dictionary add-ons do the wavy underline for incorrect spelling.