Something is Adding Suffix to URLs!

I work at home. When I try to open the company's web page, something is adding this to the URL:
/sites/all/themes/[companyname]red/images/nicemenu_arrow-right.png
At first, the page opens, then quickly flashes to a "page not found." This happens even when I type the URL on the command line.
I have deleted and reinstalled Firefox, run disk utility, and deleted the bookmarks associated with the site. It seems to have something to do with Drupal. What should I do next?

If it's something specific to Drupal, this is an issue with the web host and not you. Does this happen across browsers? Does this happen on any other website?

Others who work on that same site have not had an issue. This morning the suffix also appeared on an Apple page I tried to access. I haven't seen it anywhere else.

Try this:
https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems#w_6-reset-firefox

Wow, gsahli, that seemed to fix it. Thank you so much!