In addition to the gmail.com website, there are also Gmail client applications for various platforms (iOS, Android) that connect to the Gmail service.
If you have experience backing up gmail accounts, please help expand this section!
- http://gmvault.org/ - open source, cross-platform
- https://www.goldenhillsoftware.com/cloudpull/ - Mac only
Gmail seems to abandon browsers for no particularly good reason, given that email UIs have very simple layout / interaction needs.
- Note: This is Google's general browser support policy: support the current and previous major releases of the browser. 
- 2016-03-31 screenshot of Safari 6.1.6 (7537.78.2) with Gmail showing a warning:
This version of Safari is no longer supported. Please upgrade to a supported browser. Dismiss