Why Google is losing market share to Yahoo: Firefox.

Google suffered a noticeable defeat in November. Mozilla, the company behind the web browser Firefox, decided not to renew its relationship with the search giant, instead signing a five-year deal to make Yahoo the default search engine on the browser.

Since then, Yahoo's share of the search market has grown healthily, from 8.6% in November to 10.6% today. And Google's has correspondingly declined: In February, its market share dropped below 75% for the first time since 2008.

While Google is still the clear market leader, it is still embarrassing for the company: Search is Google's bread and butter — the company's name has become a verb synonymous with finding information online. Google's displeasure is now becoming clear, Search Engine Land reports, with the search engine prominently asking Firefox users who do not have Google set as their default search to change when they visit the site.

It's a big message at the top of search results, taking up prime advertising space and pushing the actual information down the page.

Losing Apple Safari could be next.

Google's dropping search share is painful for the company, but given that Firefox is used by only 12% of Americans, the long-term effects will be limited. But this may just be the start for Google.

Some reports say Apple is considering dropping Google as its default search engine on the iPhone's Safari web browser. It is not clear what Apple might use instead, whether Yahoo, Bing, or an in-house search, but any change would be a big loss for Google. The Wall Street Journal reports that in December more than half of all US mobile traffic came from Safari.

There's a precedent for this: Back in 2012, Apple replaced Google Maps with an in-house Apple Maps app. The software was terribly received and plagued with bugs, but Apple seems to have learned from its mistakes. The map data has been gradually improving, and Apple CEO Tim Cook eventually released an apology over the app.

Cook was so angry over the Google Maps controversy that he reportedly fired a top Apple executive over the situation. If Apple is planning to ditch Google again, it will have to ensure that whichever alternative it comes up with is up to the task.

A recent UBS research note said losing the Safari deal would not be as damaging to Google's bottom line as some are predicting — even if it would be embarrassing. Either way, this new plea to Firefox users proves that Google is concerned.