Firefox has no control over the content that websites send. It is up to Google to support Firefox for Android with regards to gmail.

Do you have any crash IDs? https://support.mozilla.org/en-US/kb/mozillacrashreporter

If the download is not opened then it is because Firefox checked with the android os and no app is registered to handle the file.

I think firefox has. Because firefox uses gecko layout engine. And chrome,opera etc uses blink which is forked from webkit. Android defualt browser uses webkit layout. So there is no problem with gmail in these browsers. I also checked with dolphin browser in android. It also worked fine for me. Then whom should i blame? If gmail uses something that works with webkit, then firefox should try forking webkit or develop something better than gecko.

Now i dont have any crash id. I will post it later.

And about the download problem, chrome and android browser downloads something, and if i tapped in the download complete notification in the android's taskbar it will directly open. In firefox mobile instead of that, when i taps on the download complete notification it will open firefox itself. If i want to open the file, i have to click on the options menu>tools>downloads and then tap on the downloaded file in firefox.

Do a search in your webkit/blink browser for "What is my useragent" without quotes. Find your user agent from one of the sites, and,copy it. Open firefox. Click menu/addons. Search for an addon called custom user agent string. Add it, than paste your chrome user agent into it for the websites that are giving you grief. Maybe that will help. This is a browser sniffer problem, not a firefox problem.

there is a copy paste problem in that add-on