Options to generate barcodes:

• Use barcode fonts. Some are free, some cost money. You get a font file (often TTF) that displays ASCII digits, letters, and some interpunctation characters as barcode fragments. You have to add start and end sequences and check digits manually. On a system lacking the fonts, you see either plaintext or just junk. This may also happen if you print to a printer with a driver that prefers printer fonts over system fonts.
• Create a vector graphic (postscript, svg, ...), composed of white and black bars of different widths. You need several bars for each character, sometimes the bar pattern also depends on the position in the bar code or on other characters. And you may need extra bars around and inside the bar code. Barcode Writer in Pure PostScript is an example for this, with the nifty trick that can run on the printer instead of the host computer.
• Create a bitmap graphic instead of a vector graphic. GD::Barcode is an old and not very clean example for such a generator.
• Use a printer that can render barcodes natively. Note that that won't help you with your browser problem.

Alexander