There was another person with this issue in the google forums that did not get a response but was asked to disable plugins. Diagnose Firefox issues using Troubleshoot Mode is the equivalent for troubleshooting this.

However I think it may have to do with gmail settings if you have tried multiple urls that lead to gmail. accounts.google.com may also get you there in the meantime.

Another explanation I ran into was to change the settings to allow multiple logins under your account settings. This can also be accessed from the above url.

I hope this helps.

Roderick van der Vaart said

I just reinstalled firefox 37.0.2 on my Macbook air. I worked a while with Chrome and use Gmail to process my email. When using Firefox I cannot open the Gmail link on the googlesearch page (like in chrome). Using Chrome provides me my email inbox. the response I get in Firefox is a dutch message which when I translate says: The page does not correctly link in a correct way. Firefox has determined that the server the request for this adrress is redirecting in an never ending action. The problem can sometimes be caused by coockies (switched off or rejected) I would like to use Gmail in Firefox but have not an idea what settings must be changed. Have you suggestion what is wrong and need to be changed ?

I do not know what has changed. I used the tip in the reply to follow the link accounts.google.com. Opened from there the gmail option. Then in another tab I went to google.com and clicked on the GMAIL link, and immediately the link was followed and my inbox was opened. I still do not know what the trick was but thanks it did help.

One more thing I noticed recently, Google changes their login. They ask for the email first and the password on a new page, this might be affecting old bookmarks as well.